The diagram above can also be used as an alternative way to convert any substance concentration (not only the normal or optimal ones) from molar to mass units and vice versa for those substances appearing in both scales, by measuring how much they are horizontally displaced from one another (representing the molar mass for that substance), and using the same distance from the concentration to be converted to determine the equivalent concentration in terms of the other unit. For example, on a certain monitor, the horizontal distance between the upper limits for parathyroid hormone in pmol/L and pg/mL may be 7 cm, with the mass concentration to the right. A molar concentration of, for example, 5 pmol/L would therefore correspond to a mass concentration located 7 cm to the right in the mass diagram, that is, approximately 45 pg/mL.


Units do not necessarily imply anything about molarity or mass.


A few substances are below this main interval, e.g.  thyroid stimulating hormone , being measured in  m U/L, or above, like  rheumatoid factor  and  CA19-9 , being measured in U/mL.


Included here are also related binding proteins, like  ferritin  and  transferrin  for iron, and  ceruloplasmin  for copper.


If  arterial / venous  is not specified for an acid–base or blood gas value, then it generally refers to arterial, and not venous which otherwise is standard for other blood tests. [ citation needed ]


Acid–base and blood gases are among the few blood constituents that exhibit substantial difference between arterial and venous values. [ 6 ]  Still, pH, bicarbonate and base excess show a high level of  inter-method reliability  between arterial and venous tests, so arterial and venous values are roughly equivalent for these. [ 44 ]


(high sensitive)


The diagrams below take inter-cycle and inter-woman variability into account in displaying reference ranges for  estradiol ,  progesterone ,  FSH  and  LH .


Also including the vitamin B 12 )-related amino acid  homocysteine .


These values (except  Hemoglobin in plasma ) are for total blood and not only blood plasma.


These values are for total blood and not only blood plasma.


Acute phase proteins  are markers of  inflammation .


Autoantibodies are usually absent or very low, so instead of being given in standard reference ranges, the values usually denote where they are said to be present, or whether the test is a  positive test . There may also be an  equivocal  interval, where it is uncertain whether there is a significantly increased level.


Electrolytes  and  metabolites :
For iron and copper, some related proteins are also included.


Assessment of kidney function  occurs in different ways, using the presence of  symptoms  and  signs , as well as measurements using urine tests, blood tests, and medical imaging.


Functions of a healthy kidney  include maintaining a person's   fluid balance , maintaining an  acid-base balance ; regulating electrolytes  sodium ,  and other  electrolytes ;  clearing   toxins ; regulating  blood pressure ; and regulating  hormones , such as  erythropoietin ; and activation of  vitamin D . The kidney is also involved in maintaining blood pH balance.


The functions of the kidney include maintenance of  acid-base balance ; regulation of  fluid balance ; regulation of  sodium ,  potassium , and other  electrolytes ;  clearance  of  toxins ; absorption of  glucose ,  amino acids , and other small molecules; regulation of  blood pressure ; production of various  hormones , such as  erythropoietin ; and activation of  vitamin D .


The  Glomerular filtration rate  (GFR) is regarded as the best overall measure of the kidney's ability to carry out these numerous functions. An estimate of the GFR is used clinically to determine the degree of kidney impairment and to track the progression of the disease. The GFR, however, does not reveal the source of the kidney disease. This is accomplished by urinalysis, measurement of urine protein excretion, kidney imaging, and, if necessary, kidney biopsy. [ 1 ]


Much of renal physiology is studied at the level of the  nephron  – the smallest functional unit of the kidney. Each nephron begins with a  filtration  component that filters the  blood  entering the kidney. This filtrate then flows along the length of the nephron, which is a tubular structure lined by a single layer of specialized  cells  and surrounded by  capillaries . The major functions of these lining cells are the  reabsorption  of water and small molecules from the filtrate into the blood, and the  secretion  of wastes from the blood into the  urine . [ citation needed ]


Proper function of the kidney requires that it receives and adequately filters blood. This is performed at the microscopic level by many hundreds of thousands of filtration units called  renal corpuscles , each of which is composed of a  glomerulus  and a  Bowman's capsule . A global assessment of renal function is often ascertained by estimating the rate of filtration, called the  glomerular filtration rate  (GFR).


Clinical assessment can be used to assess the function of the kidneys. This is because a person with abnormally functioning kidneys may have symptoms that develop. For example, a person with chronic kidney disease may develop  oedema  due to failure of the kidneys to regulate water balance. They may develop evidence of chronic kidney disease, that can be used to assess its severity, for example  high blood pressure ,  osteoporosis  or  anaemia . If the kidneys are unable to excrete  urea , a person may develop a widespread  itch  or  confusion . [ citation needed ]


Part of the assessment of kidney function includes the measurement of urine and its contents. Abnormal kidney function may cause too much or too little urine to be produced. The ability of the kidneys to filter protein is often measured, as  urine albumin  or  urine protein  levels, [ 2 ]  measured either at a single instance or, because of variation throughout the day, as 24-hour urine tests. [ citation needed ]


Blood tests are also used to assess kidney function. These include tests that are intended to directly measure the function of the kidneys, as well as tests that assess the function of the kidneys by looking for evidence of problems associated with abnormal function. One of the measures of kidney function is the glomerular filtration rate (GFR). Other tests that can assess the function of the kidneys include assessment of  electrolyte  levels such as  potassium  and  phosphate , assessment of acid-base status by the measurement of  bicarbonate  levels from a vein, and assessment of the  full blood count  for  anaemia . [ citation needed ]


The glomerular filtration rate (GFR) describes the volume of fluid filtered from the  renal  (kidney)  glomerular  capillaries into the  Bowman's capsule  per unit time. [ 3 ]  Creatinine clearance (C Cr ) is the volume of  blood plasma  that is cleared of  creatinine  per unit time and is a useful measure for approximating the GFR. Creatinine clearance exceeds GFR due to creatinine secretion, [ 4 ]  which can be blocked by  cimetidine .   Both GFR and C Cr  may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result ( eGFR  and  eC Cr ) The results of these tests are used to assess the excretory function of the kidneys.  Staging  of  chronic kidney disease  is based on categories of GFR as well as  albuminuria  and cause of  kidney disease . [ 2 ]


Central to the physiologic maintenance of GFR is the differential basal tone of the afferent and efferent arterioles (see diagram). In other words, the filtration rate is dependent on the difference between the higher blood pressure created by vasoconstriction of the input or afferent arteriole versus the lower blood pressure created by lesser vasoconstriction of the output or efferent arteriole.


GFR is equal to the  renal clearance ratio  when any solute is freely filtered and is neither reabsorbed nor secreted by the kidneys. The rate therefore measured is the quantity of the substance in the urine that originated from a calculable volume of blood. Relating this principle to the below equation – for the substance used, the product of urine concentration and urine flow equals the mass of substance excreted during the time that urine has been collected. This mass equals the mass filtered at the glomerulus as nothing is added or removed in the nephron. Dividing this mass by the plasma concentration gives the volume of plasma which the mass must have originally come from, and thus the volume of plasma fluid that has entered Bowman's capsule within the aforementioned period of time. The GFR is typically recorded in units of  volume per time , e.g., milliliters per minute ( mL / min ). Compare to  filtration fraction . [ citation needed ]


There are several different techniques used to calculate or estimate the glomerular filtration rate (GFR or eGFR). The above formula only applies for GFR calculation when it is equal to the clearance rate.


The normal range of GFR, adjusted for  body surface area , is 100–130 average 125 (mL/min)/(1.73 m 2 ) in men and 90–120 (mL/min)/(1.73 m 2 ) in women younger than the age of 40. In children, GFR measured by inulin clearance is 110 (mL/min)/(1.73 m 2 ) until 2 years of age in both sexes, and then it progressively decreases. After age 40, GFR decreases progressively with age, by 0.4–1.2 mL/min per year. [ citation needed ]


Estimated GFR (eGFR) is now recommended by clinical practice guidelines and regulatory agencies for routine evaluation of GFR whereas measured GFR (mGFR) is recommended as a confirmatory test when more accurate assessment is required. [ 5 ]


The kidney function can also be assessed with  medical imaging . Some forms of imaging, such as  kidney ultrasound  or  CT scans , may assess kidney function by indicating chronic disease that can impact function, by showing a small or shrivelled kidney. [ citation needed ] . Other tests, such as  nuclear medicine  tests, directly assess the function of the kidney by measuring the perfusion and excretion of radioactive substances through the kidneys. [ citation needed ]


A decreased renal function can be caused by many types of  kidney disease . Upon presentation of decreased renal function, it is recommended to perform a  history  and  physical examination , as well as performing a  renal ultrasound  and a  urinalysis . [ citation needed ]  The most relevant items in the history are  medications ,  edema ,  nocturia , gross  hematuria ,  family history  of kidney disease,  diabetes  and  polyuria . The most important items in a physical examination are signs of  vasculitis ,  lupus erythematosus ,  diabetes ,  endocarditis  and  hypertension . [ citation needed ]


A urinalysis is helpful even when not showing any pathology, as this finding suggests an extrarenal etiology.  Proteinuria  and/or  urinary sediment  usually indicates the presence of  glomerular disease .  Hematuria  may be caused by glomerular disease or by a disease along the  urinary tract . [ citation needed ]


The most relevant assessments in a  renal ultrasound  are renal sizes,  echogenicity  and any signs of  hydronephrosis . Renal enlargement usually indicates diabetic nephropathy,  focal segmental glomerular sclerosis  or  myeloma . Renal atrophy suggests longstanding chronic renal disease. [ citation needed ]


Risk factors for kidney disease include diabetes, high blood pressure, family history, older age, ethnic group and smoking.
For most patients, a GFR over 60 (mL/min)/(1.73 m 2 ) is adequate. But significant decline of the GFR from a previous test result can be an early indicator of kidney disease requiring medical intervention. The sooner kidney dysfunction is diagnosed and treated the greater odds of preserving remaining nephrons, and preventing the need for dialysis.


The  severity of chronic kidney disease  (CKD) is described by six stages; the most severe three are defined by the MDRD-eGFR value, and first three also depend on whether there is other evidence of kidney disease (e.g.,  proteinuria ):


Note: others add a "T" to patients who have had a transplant regardless of stage.


Not all clinicians agree with the above classification, suggesting that it may mislabel patients with mildly reduced kidney function, especially the elderly, as having a disease. [ 6 ] [ 7 ]  A conference was held in 2009 regarding these controversies by Kidney Disease: Improving Global Outcomes (KDIGO) on CKD: Definition, Classification and Prognosis, gathering data on CKD prognosis to refine the definition and staging of CKD. [ 8 ]


Renal functions  include maintaining an  acid–base balance ; regulating  fluid balance ; regulating  sodium ,  potassium , and other  electrolytes ;  clearing   toxins ; absorption of  glucose ,  amino acids , and other small molecules;  regulation of  blood pressure ; production of various  hormones , such as  erythropoietin ; and activation of  vitamin D .


The  kidney  has many functions, which a well-functioning kidney realizes by filtering blood in a process known as  glomerular filtration . A major measure of  kidney function  is the  glomerular filtration rate  ( GFR ).
The glomerular filtration rate is the flow rate of filtered fluid through the kidney. The  creatinine clearance rate  ( C Cr  or  CrCl ) is the volume of  blood plasma  that is cleared of  creatinine  per unit time and is a useful measure for approximating the GFR. Creatinine clearance exceeds GFR due to creatinine secretion, [ 1 ]  which can be blocked by  cimetidine .  Both GFR and C Cr  may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result ( eGFR  and  eC Cr ) The results of these tests are used to assess the excretory function of the kidneys.  Staging  of  chronic kidney disease  is based on categories of GFR as well as  albuminuria  and cause of  kidney disease . [ 2 ]


Estimated GFR (eGFR) is now recommended by clinical practice guidelines and regulatory agencies for routine evaluation of GFR whereas measured GFR (mGFR) is recommended as a confirmatory test when more accurate assessment is required. [ 3 ]


Glomerular filtration rate (GFR) is the volume of fluid filtered from the  renal  (kidney)  glomerular  capillaries into the  Bowman's capsule  per unit time. [ 4 ]   Central to the physiologic maintenance of GFR is the differential basal tone of the afferent (input) and efferent (output) arterioles (see diagram). In other words, the filtration rate is dependent on the difference between the higher blood pressure created by vasoconstriction of the afferent arteriole versus the lower blood pressure created by lesser vasoconstriction of the efferent arteriole. [ citation needed ]


GFR is equal to the  renal clearance rate  when any solute is freely filtered and is neither reabsorbed nor secreted by the kidneys. The rate therefore measured is the quantity of the substance in the urine that originated from a calculable volume of blood. Relating this principle to the below equation – for the substance used, the product of urine concentration and urine flow equals the mass of substance excreted during the time that urine has been collected. This mass equals the mass filtered at the glomerulus as nothing is added or removed in the nephron. Dividing this mass by the plasma concentration gives the volume of plasma which the mass must have originally come from, and thus the volume of plasma fluid that has entered Bowman's capsule within the aforementioned period of time. The GFR is typically recorded in units of  volume per time , e.g., milliliters per minute (mL/min). Compare to  filtration fraction .


There are several different techniques used to calculate or estimate the glomerular filtration rate (GFR or eGFR). The above formula only applies for GFR calculation when it is equal to the Clearance Rate.


In clinical practice, however,  creatinine clearance  or estimates of creatinine clearance based on the serum creatinine level are used to measure GFR. [ citation needed ]  Creatinine is produced naturally by the body ( creatinine   is a breakdown product of  creatine phosphate , which is found in muscle). It is freely filtered by the glomerulus, but also actively  secreted by the peritubular capillaries  in very small amounts such that creatinine clearance overestimates actual GFR by 10–20%. This margin of error is acceptable, considering the ease with which creatinine clearance is measured. Unlike precise GFR measurements involving constant infusions of inulin, creatinine is already at a steady-state concentration in the blood, and so measuring creatinine clearance is much less cumbersome.  However, creatinine estimates of GFR have their limitations. All of the estimating equations depend on a prediction of the 24-hour creatinine excretion rate, which is a function of muscle mass which is quite variable.  One of the equations, the Cockcroft and Gault equation (see below) does not correct for race. With a higher muscle mass, serum creatinine will be higher for any given rate of clearance.


The GFR can be determined by injecting  inulin  or the inulin-analog  sinistrin  into the blood stream.  Since both inulin and sinistrin are neither reabsorbed nor secreted by the kidney after glomerular filtration, their rate of excretion is directly proportional to the rate of filtration of water and solutes across the glomerular filter. Incomplete urine collection is an important source of error in inulin clearance measurement. [ 5 ]
Using inulin to measure  kidney function  is the  "gold standard"  for comparison with other means of estimating  glomerular filtration rate . [ 6 ]  In 2018, the French  pharmacovigilance  agency withdrew  inulin  and  sinistrin -based products from the market after some patients experienced hypersensitivity reactions including a fatal outcome. [ 7 ]  Consequently, the  contrast agents   Iohexol  and  Iothalamate  have become more popular alternatives to determine GFR and are considered to show sufficient accuracy to determine GFR. [ 8 ]


GFR can be accurately measured using radioactive substances, in particular  chromium-51  and  technetium-99m . These come close to the ideal properties of inulin (undergoing only glomerular filtration) but can be measured more practically with only a few urine or blood samples. [ 9 ]  Measurement of renal or plasma clearance of  51 Cr- EDTA  is widely used in Europe but not available in the United States, where  99m Tc- DTPA  may be used instead. [ 10 ]  Renal and plasma clearance  51 Cr-EDTA has been shown to be accurate in comparison with the gold standard, inulin. [ 11 ] [ 12 ] [ 6 ]  Use of  51 Cr‑EDTA is considered a reference standard measure in UK guidance. [ 13 ]


Problems with creatinine (varying muscle mass, recent meat ingestion (much less dependent on the diet than urea), etc.) have led to evaluation of alternative agents for estimation of GFR.  One of these is  cystatin C , a ubiquitous protein secreted by most cells in the body (it is an inhibitor of cysteine protease). [ 14 ]


Cystatin C is freely filtered at the glomerulus.  After filtration, Cystatin C is reabsorbed and catabolized by the tubular epithelial cells, with only small amounts excreted in the urine.  Cystatin C levels are therefore measured not in the urine, but in the bloodstream.


Equations have been developed linking estimated GFR to serum cystatin C levels. [ 15 ]  Most recently, some proposed equations have combined sex, age, adjusted cystatin C and creatinine. In 2022, the National Kidney Foundation (NKF) and American Society of Nephrology (ASN)'s Joint Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Diseases recommended national efforts to facilitate increased, routine, and timely use of cystatin C. They noted that cystatin C would be useful particularly to confirm estimated GFR in adults who are at risk for or have chronic kidney disease. They suggested that combining filtration markers (creatinine and cystatin C) is more accurate and would support better clinical decisions than either marker alone. [ 16 ]


INTEGRATION


More precisely, GFR is the fluid flow rate between the glomerular capillaries and the Bowman's capsule:


Where:


Because this constant is a measurement of  hydraulic conductivity  multiplied by the capillary surface area, it is almost impossible to measure physically.  However, it can be determined experimentally.  Methods of determining the GFR are listed in the above and below sections and it is clear from our equation that

 K

 f

 {\displaystyle K_{f}}

  can be found by dividing the experimental GFR by the net filtration pressure: [ 17 ]


The hydrostatic pressure within the glomerular capillaries is determined by the pressure difference between the fluid entering immediately from the  afferent arteriole  and leaving through the  efferent arteriole .  The pressure difference is approximated by the product of the total resistance of the respective arteriole and the flux of blood through it: [ 18 ]


The pressure in the Bowman's capsule and proximal tubule can be determined by the difference between the pressure in the Bowman's capsule and the descending tubule: [ 18 ]


Blood plasma has a good many proteins in it and they exert an inward directed force called the  osmotic pressure  on the water in hypotonic solutions across a membrane, i.e., in the Bowman's capsule.  Because plasma proteins are virtually incapable of escaping the glomerular capillaries, this oncotic pressure is defined, simply, by the ideal gas law: [ 17 ] [ 18 ]


This value is almost always taken to be equal to zero because in a healthy  nephron , there should be no proteins in the Bowman's capsule. [ 17 ]


The filtration fraction is the amount of plasma that is actually filtered through the kidney. This can be defined using the equation:


FF =  GFR / RPF


Normal human FF is 20%.


C x =( U x )  V / P x


In clinical practice, however,  creatinine clearance  or estimates of creatinine clearance based on the serum creatinine level are used to measure GFR. Creatinine is produced naturally by the body ( creatinine   is a breakdown product of  creatine phosphate , which is found in muscle). It is freely filtered by the glomerulus, but also actively  secreted by the peritubular capillaries  in very small amounts such that creatinine clearance overestimates actual GFR by 10–20%. This margin of error is acceptable, considering the ease with which creatinine clearance is measured. Unlike precise GFR measurements involving constant infusions of inulin, creatinine is already at a steady-state concentration in the blood, and so measuring creatinine clearance is much less cumbersome.  However, creatinine estimates of GFR have their limitations. All of the estimating equations depend on a prediction of the 24-hour creatinine excretion rate, which is a function of muscle mass which is quite variable.  The Cockcroft-Gault and CKD-EPI 2021 equations (see below) do not correct for race. With a higher muscle mass, serum creatinine will be higher for any given rate of clearance. [ 19 ]


A common mistake made when just looking at serum creatinine is the failure to account for muscle mass.  Hence, an older woman with a serum creatinine of 1.4 mg/dL may actually have a moderately severe  chronic kidney disease , whereas a young muscular male can have a normal level of renal function at this serum creatinine level.  Creatinine-based equations should be used with caution in  cachectic  patients and patients with  cirrhosis .  They often have very low muscle mass and a much lower creatinine excretion rate than predicted by the equations below, such that a cirrhotic patient with a serum creatinine of 0.9 mg/dL may have a moderately severe degree of chronic kidney disease.


One method of determining GFR from creatinine is to collect urine (usually for 24 h) to determine the amount of creatinine that was removed from the blood over a given time interval.  If one removes 1440 mg in 24 h, this is equivalent to removing 1 mg/min.  If the blood concentration is 0.01 mg/mL (1 mg/dL), then one can say that 100 mL/min of blood is being "cleared" of creatinine, since, to get 1 mg of creatinine, 100 mL of blood containing 0.01 mg/mL would need to have been cleared.


Creatinine clearance (C Cr ) is calculated from the creatinine concentration in the collected urine sample (U Cr ),  urine flow rate  (V dt ), and the plasma concentration (P Cr ). Since the product of urine concentration and urine flow rate yields creatinine excretion rate, which is the rate of removal from the blood, creatinine clearance is calculated as removal rate per min (U Cr ×V dt ) divided by the plasma creatinine concentration. This is commonly represented mathematically as


Example: A person has a plasma creatinine concentration of 0.01 mg/mL and in 1 hour produces 60 mL of urine with a creatinine concentration of 1.25 mg/mL.


The common procedure involves undertaking a 24-hour urine collection, from empty-bladder one morning to the contents of the bladder the following morning, with a comparative blood test then taken.  The urinary flow rate is still calculated per minute, hence:


To allow comparison of results between people of different sizes, the C Cr  is often corrected for the  body surface area  (BSA) and expressed compared to the average sized man as mL/min/1.73 m 2 . While most adults have a BSA that approaches 1.7 m 2  (1.6 m 2  to 1.9 m 2 ), extremely obese or slim patients should have their C Cr  corrected for their  actual  BSA.


Twenty-four-hour urine collection to assess creatinine clearance is no longer widely performed, due to difficulty in assuring complete specimen collection.  To assess the adequacy of a complete collection, one always calculates the amount of creatinine excreted over a 24-hour period.  This amount varies with muscle mass and is higher in young people/old, and in men/women.  An unexpectedly low or high 24-hour creatinine excretion rate voids the test.  Nevertheless, in cases where estimates of creatinine clearance from serum creatinine are unreliable, creatinine clearance remains a useful test. These cases include "estimation of GFR in individuals with variation in dietary intake (vegetarian diet, creatine supplements) or muscle mass (amputation, malnutrition, muscle wasting), since these factors are not specifically taken into account in prediction equations." [ 20 ]


A number of formulae have been devised to estimate GFR or C cr  values on the basis of serum creatinine levels. Where not otherwise stated serum creatinine is assumed to be stated in mg/dL, not μmol/L—divide by 88.4 to convert from μmol/Lto mg/dL.


A commonly used surrogate marker for the estimation of  creatinine clearance  is the Cockcroft–Gault (CG) formula, which in turn estimates GFR in ml/min: [ 21 ]  It is named after the scientists, the asthmologist  Donald William Cockcroft  [ de ]  (b. 1946) and the nephrologist  Matthew Henry Gault  [ de ]  (1925–2003), who first published the formula in 1976, and it employs serum  creatinine  measurements and a patient's weight to predict the creatinine clearance. [ 22 ] [ 23 ]
The formula, as originally published, is:


When serum creatinine is measured in μmol/L:


One interesting feature of the Cockcroft and Gault equation is that it shows how dependent the estimation of CCr is based on age. The age term is (140 – age).  This means that a 20-year-old person (140 – 20 = 120) will have twice the creatinine clearance as an 80-year-old (140 – 80 = 60) for the same level of serum creatinine.  The C-G equation assumes that a woman will have a 15% lower creatinine clearance than a man at the same level of serum creatinine.


Another formula for calculating the GFR is the one developed by the  Modification of Diet in Renal Disease Study Group . [ 24 ]  Most laboratories in Australia, [ 25 ]  and the United Kingdom now calculate and report the estimated GFR along with creatinine measurements and this forms the basis of diagnosis of  chronic kidney disease . [ 26 ] [ 27 ]  The adoption of the automatic reporting of MDRD-eGFR has been widely criticised. [ 28 ] [ 29 ] [ 30 ]


The most commonly used formula is the "4-variable MDRD", which estimates GFR using four variables: serum creatinine, age, ethnicity, and gender. [ 31 ]  The original MDRD used six variables with the additional variables being the  blood urea nitrogen  and  albumin  levels. [ 24 ]  The equations have been validated in patients with chronic kidney disease; however, both versions underestimate the GFR in healthy patients with GFRs over 60 mL/min. [ 32 ] [ 33 ]  The equations have not been validated in acute renal failure.


For creatinine in μmol/L:


For creatinine in mg/dL:


A more elaborate version of the MDRD equation also includes  serum albumin  and  blood urea nitrogen  (BUN) levels:


These MDRD equations are to be used only if the laboratory has NOT calibrated its serum creatinine measurements to isotope dilution mass spectrometry (IDMS).  When IDMS-calibrated serum creatinine is used (which is about 6% lower), the above equations should be multiplied by 175/186 or by 0.94086. [ 34 ]


Since these formulae do not adjust for body size, results are given in units of mL/min per 1.73 m 2 , 1.73 m 2  being the estimated body surface area of an adult with a mass of 63 kg and a height of 1.7 m.


The CKD-EPI  (Chronic Kidney Disease Epidemiology Collaboration) formula was first published in May 2009.  It was developed in an effort to create a formula more accurate than the MDRD formula, especially when actual GFR is greater than 60 mL/min per 1.73 m 2 . This is the formula currently recommended by NICE in the UK. [ 27 ]


Researchers pooled data from multiple studies to develop and validate this new equation.  They used 10 studies that included 8254 participants, randomly using 2/3 of the data sets for development and the other 1/3 for internal validation. Sixteen additional studies, which included 3896 participants, were used for external validation.


The CKD-EPI equation performed better than the MDRD (Modification of Diet in Renal Disease Study) equation, especially at higher GFR, with less bias and greater accuracy. When looking at NHANES (National Health and Nutrition Examination Survey) data, the median estimated GFR was 94.5 mL/min per 1.73 m 2  vs. 85.0 mL/min per 1.73 m 2 , and the prevalence of chronic kidney disease was 11.5% versus 13.1%. Despite its overall superiority to the MDRD equation, the CKD-EPI equations performed poorly in certain populations, including black women, the elderly and the obese, and was less popular among clinicians than the MDRD estimate. [ 35 ]


The 2009 CKD-EPI equation is:


where SCr is serum creatinine (mg/dL), k is 0.7 for females and 0.9 for males, a is −0.329 for females and −0.411 for males, min indicates the minimum of SCr/k or 1, and max indicates the maximum of SCr/k or 1.


As separate equations for different populations:
For creatinine (IDMS calibrated) in mg/dL:


This formula was developed by Levey et al. [ 36 ]


The 2009 CKD-EPI formula was suggested to improve cardiovascular risk prediction over the MDRD Study formula in a middle-age population. [ 37 ]


The 2021 CKD-EPI formula [ 38 ]  does not include a race coefficient (see discussion below).
The 2021 CKD-EPI equation is:


where SCr is serum creatinine (mg/dL), k is 0.7 for females and 0.9 for males, a is −0.241 for females and −0.302 for males, min indicates the minimum of SCr/k or 1, and max indicates the maximum of SCr/k or 1.


Another estimation tool to calculate GFR is the Mayo Quadratic formula. This formula was developed by Rule et al., [ 32 ]  in an attempt to better estimate GFR in patients with preserved kidney function.  It is well recognized that the MDRD formula tends to underestimate GFR in patients with preserved kidney function. Studies in 2008 found that the Mayo Clinic Quadratic Equation compared moderately well with radionuclide GFR, but had inferior bias and accuracy than the MDRD equation in a clinical setting. [ 39 ] [ 40 ]


The equation is:


If Serum Creatinine < 0.8 mg/dL, use 0.8 mg/dL for Serum Creatinine.


In children, the Schwartz formula is used. [ 41 ] [ 42 ]  This employs the serum  creatinine  (mg/dL), the child's height (cm) and a constant to estimate the glomerular filtration rate:


The method of selection of the constant  k  has been questioned as being dependent upon the gold-standard of renal function used (i.e. inulin clearance, creatinine clearance, etc.) and also may be dependent upon the urinary flow rate at the time of measurement. [ 44 ]


In 2009 the formula was updated to use standardized serum creatinine (recommend  k =0.413) and additional formulas that allow improved precision were derived if serum  cystatin C  is measured in addition to serum creatinine. [ 45 ]


One problem with any creatinine-based equation for GFR is that the methods used to assay creatinine in the blood differ widely in their susceptibility to non-specific chromogens, which cause the creatinine value to be overestimated.  In particular, the MDRD equation was derived using serum creatinine measurements that had this problem.  The NKDEP program in the United States has attempted to solve this problem by trying to get all laboratories to calibrate their measures of creatinine to a "gold standard", which in this case is  isotope dilution mass spectrometry  (IDMS).  In late 2009 not all labs in the U.S. had changed over to the new system.  There are two forms of the MDRD equation that are available, depending on whether or not creatinine was measured by an IDMS-calibrated assay.  The CKD-EPI equation is designed to be used with IDMS-calibrated serum creatinine values only. [ citation needed ]


The normal range of GFR, adjusted for  body surface area , is 100–130 average 125 mL/min/1.73m 2  in men and 90–120 ml/min/1.73m 2  in women younger than the age of 40. In children, GFR measured by inulin clearance is 110 mL/min/1.73 m 2  until 2 years of age in both sexes, and then it progressively decreases. After age 40, GFR decreases progressively with age, by 0.4–1.2 mL/min per year. [ citation needed ]


Risk factors for kidney disease include diabetes, high blood pressure, family history, older age, ethnic group and smoking.
For most patients, a GFR over 60 mL/min/1.73 m 2  is adequate. But significant decline of the GFR from a previous test result can be an early indicator of kidney disease requiring medical intervention. The sooner kidney dysfunction is diagnosed and treated the greater odds of preserving remaining nephrons, and preventing the need for dialysis. [ citation needed ]


Not all clinicians agree with the above classification, suggesting that it may mislabel patients with mildly reduced kidney function, especially the elderly, as having a disease. [ 46 ] [ 47 ]  A conference was held in 2009 regarding these controversies by Kidney Disease: Improving Global Outcomes (KDIGO) on CKD: Definition, Classification and Prognosis, gathering data on CKD prognosis to refine the definition and staging of CKD. [ 48 ]


In 2017, Beth Israel Deaconess Medical Center dropped the Black race coefficient in their estimated glomerular filtration rate (eGFR) report, resulting in a steady increase in the percentage of Black patients listed before starting dialysis. Hoenig et al said on the topic "Race is a social construct that cannot be measured, can be used imprecisely and may contribute to disparities in kidney transplant access for Black patients." [ 49 ]


In 2020, Vyas et al published an article in  The New England Journal of Medicine  criticizing the use of race in eGFR calculations which resulted in higher reported eGFR values for black-identifying patients. They noted that "The algorithm developers justified these outcomes with evidence of higher average serum creatinine concentrations among black people than among white people. Explanations that have been given for this finding include the notion that black people release more creatinine into their blood at baseline, in part because they are reportedly more muscular. Analyses have cast doubt on this claim, but the "race-corrected" eGFR remains the standard." They concluded saying "As long as uncertainty persists about the cause of racial differences in serum creatinine levels, we should favor practices that may alleviate health inequities over those that may exacerbate them." [ 50 ]


In February 2022, the National Kidney Foundation (NKF) and American Society of Nephrology (ASN)'s Joint Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Diseases recommended use of the 2021 CKD-EPI equation which discontinues using a race modifier. [ 16 ]


In July 2022 the  OPTN  Board eliminated race-based calculations for  transplant  candidate listing across all transplant hospitals in the US. [ 51 ]


Reptilase time  ( RT ) is a  blood test  used to detect deficiency or abnormalities in  fibrinogen , [ 1 ] [ 2 ]  especially in cases of  heparin  contamination.


Reptilase , an enzyme found in the  venom  of  Bothrops snakes , has activity similar to  thrombin . Unlike thrombin, reptilase is resistant to inhibition by  antithrombin III . Thus, the reptilase time is not prolonged in blood samples containing heparin,  hirudin , or  direct thrombin inhibitors , whereas the  thrombin time  will be prolonged in these samples. Reptilase also differs from thrombin by releasing  fibrinopeptide A , but not  fibrinopeptide B , in its cleavage of  fibrinogen . [ citation needed ]


The  reticulocyte production index  ( RPI ), also called a  corrected reticulocyte count  ( CRC ), is a calculated value used in the diagnosis of  anemia . This calculation is necessary because the raw  reticulocyte  count is misleading in anemic patients. The problem arises because the reticulocyte count is not really a  count  but rather a  percentage : it reports the number of reticulocytes as a percentage of the number of red blood cells. In anemia, the patient's red blood cells are depleted, creating an erroneously  elevated reticulocyte count .


Reticulocytes  are newly produced red blood cells. They are slightly larger than totally mature red blood cells, and have some residual ribosomal  RNA . The presence of RNA allows a visible blue stain to bind or, in the case of fluorescent dye, result in a different brightness. This allows them to be detected and counted as a distinct population. [ 2 ]


The RPI is used to assess whether the  bone marrow  is producing an appropriate response to an anemic state. Reticulocyte production should increase in response to any loss of red blood cells. It should increase within 2–3 days of a major acute  hemorrhage , for instance, and reach its peak in 6–10 days. [ 3 ]  If reticulocyte production is not raised in response to anemia, then the anemia may be due to an acute cause with insufficient time to compensate, or there is a defect with red blood cell production in the bone marrow. Marrow defects include nutritional deficiencies (i.e. iron, folate, or B 12 ) or insufficient  erythropoietin , the stimulus for red blood cell production.  Reticulocytopenia , or "aplastic crisis", is the medical term for an abnormal decrease of reticulocytes in the body
The reticulocyte production index may find new use as a more reliable detector of erythropoietin-doping in athletes. The use of this method is referred to as "biological passport." [ citation needed ]


Reticulocyte Production Index is calculated as follows:


1.

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 =
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 ∗

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 i
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 N
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 {\displaystyle CorrectedReticPercentage=ReticPercentage*{Hematocrit \over NormalHematocrit}}


This calculation is to correct for the severity of the anemia.
A value of 45% (or 0,45  L/L ) is usually used as a normal hematocrit for males. [ 4 ]


2. The next step is to correct for the longer life span of prematurely released reticulocytes in the blood—a phenomenon of increased red blood cell production. This relies on a table:


So,  in a person whose reticulocyte percentage is 5%, hemoglobin 7.5 g/dL, hematocrit 25%, the RPI would be:


R
 P
 I
 =

 C
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 R
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 M
 a
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 C
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 o
 n

 {\displaystyle RPI={CorrectedReticPercentage \over MaturationCorrection}}

   → RPI

 =

 5
 ∗

 25
 45

 2

 =

 {\displaystyle ={{5*{25 \over 45}} \over 2}=}

 1.4


Alternatively some books provide the following formula and is called  Reticulocyte Index (RI) :


Whereas normal reticulocytes lose their RNA within 24 hours, a severely anemic patient with a full erythropoietin response will release reticulocytes that take from 2-3 days to lose their RNA. This has the effect of raising the reticulocyte count simply because reticulocytes produced on any single
day will spend more than 1 day in circulation as reticulocytes and, therefore, will be counted for 2 or more days. The  simplest  method for correcting the reticulocyte count, to obtain a more accurate daily production index, is to  divide the corrected count by a factor of 2  ( or multiply with ½ ) whenever polychromasia (the presence of immature marrow reticulocytes or "shift" cells) is observed on the smear or the immature fraction on the automated counter is increased. [ 5 ]   [ 6 ]   [ 7 ]


R
 I
 =
 R
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 ∗

 H
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 i
 t

 N
 o
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 a
 l
 H
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 m
 a
 t
 o
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 i
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 ∗
 0.5

 {\displaystyle RI=ReticPercentage*{Hematocrit \over NormalHematocrit}*0.5}

   →

 R
 I
 =
 5
 ∗

 25
 45

 ∗
 0.5
 =

 {\displaystyle RI=5*{25 \over 45}*0.5=}

 1.4


Interpretation of these values are not standard and vary based on specific laboratory values and clinical context. [ 9 ]


The  ristocetin-induced platelet aggregation  ( RIPA ) is an ex vivo assay for live platelet function. It measures platelet aggregation with the help of  von Willebrand factor  (vWF) and exogenous antibiotic  ristocetin  added in a graded fashion. [ 1 ]  It is similar to the ristocetin cofactor assay but has the added benefit in that it helps in the diagnosis of type 2B/pseudo  von Willebrand disease  (vWD) and  Bernard–Soulier syndrome  because it uses patient's live endogenous platelets, whereas ristocetin cofactor assay tests the function of only the vWF and not the platelets. Ristocetin cofactor assay uses the patient's platelet poor plasma (with vWF but no platelets) and adds ristocetin and exogenous formalin-fixed platelets which can passively agglutinate (but not actively aggregate, as they are dead). Formalin does not allow the extrinsic platelets to secrete the vWF of their α-granules, and thus only the activity of the intrinsic vWF is tested. [ citation needed ]


In an unknown fashion, the antibiotic  ristocetin  causes von Willebrand factor to bind the platelet receptor  glycoprotein Ib  (GpIb), so when ristocetin is added to normal blood, it causes agglutination of fixed platelets or initiates the initial agglutination phase of aggregation of live platelets. [ citation needed ]


The results of the ristocetin-induced platelet aggregation in some characteristic diseases are the following:


INTERPRETATION OF TEST
RAT+ Ve= normal (gp1b & vWF present)
RAT-ve=abnormal(gp1b & vWF absent)


Schmerber v. California , 384 U.S. 757 (1966), was a  landmark [ 1 ]   United States Supreme Court  case in which the Court clarified the application of the  Fourth Amendment 's protection against  warrantless  searches and the  Fifth Amendment  right against  self-incrimination  for searches that intrude into the human body. Until  Schmerber , the Supreme Court had not yet clarified whether state police officers must procure a search warrant before  taking blood samples  from criminal suspects. Likewise, the Court had not yet clarified whether blood evidence taken against the wishes of a criminal suspect may be used against that suspect in the course of a criminal prosecution. [ fn 1 ]


In a 5–4 opinion, the Court held that forced extraction and analysis of a blood sample is not compelled testimony; therefore, it does not violate the Fifth Amendment right against self-incrimination. [ 5 ]  The Court also held that intrusions into the human body ordinarily require a search warrant. [ 6 ]  However, the Court ruled that the involuntary, warrantless blood sample taken in this case was justified under the Fourth Amendment's  exigent circumstances  exception because evidence of blood alcohol would be destroyed by the body's natural  metabolic  processes if the officers were to wait for a warrant. [ 7 ]  In 2013, the Supreme Court clarified in  Missouri v. McNeely  that the natural metabolism of alcohol in the bloodstream is not a  per se  exigency that would always justify warrantless blood tests of individuals suspected of driving under the influence of alcohol. [ 8 ]


In the years following the Court's decision in  Schmerber , many legal scholars feared the ruling would be used to limit  civil liberties . [ 9 ]  Other scholars, including Nita A. Farahany, Benjamin Holley, and John G. New, have suggested courts may use the ruling in  Schmerber  to justify the use of  mind reading  devices against criminal suspects. [ 10 ]  Because the Court's ruling in  Schmerber  prohibited the use of warrantless blood tests in most circumstances, some commentators argue that the decision was responsible for the proliferation of  breathalyzers  to test for alcohol and  urine analyses  to test for controlled substances in criminal investigations. [ 11 ]


In the 1950s, the  Supreme Court of the United States  issued two key rulings clarifying the constitutionality of physical intrusions into the human body by police and other government agents. In  Rochin v. California , police officers broke into the home of an individual suspected of selling narcotics and observed him place several small objects into his mouth. [ 12 ]  Officers were unable to force his mouth open, so they transported him to a local hospital where his stomach was pumped against his will. [ 13 ]  A unanimous Supreme Court held the involuntary stomach pump was an unlawful violation of  substantive due process  because it "shocked the conscience", and was so "brutal" and "offensive" that it did not comport with traditional ideas of fair play and decency. [ 14 ]  In 1957, the Court held in  Breithaupt v. Abram  that involuntary blood samples "taken by a skilled technician" neither "shocked the conscience" nor violated  substantive due process . [ 15 ]  In  Breithaupt , police took a blood sample from a patient suspected of driving under the influence of alcohol while he lay unconscious in a hospital. [ 16 ]  The Court held that the blood samples were justified, in part, because "modern community living requires modern scientific methods of crime detection." [ 3 ]  Additionally, the Court mentioned in  dicta  that involuntary blood samples may violate the constitution if officers do not provide "every proper medical precaution" to the accused. [ 17 ]


Until the twentieth century, courts would admit evidence at trial even if it was seized in violation of the Fourth Amendment. [ 18 ]  Although the Supreme Court developed an  exclusionary rule  for federal cases in  Weeks v. United States  and  Silverthorne Lumber Co. v. United States , [ 19 ]  the Court held in 1949 that the exclusionary rule did not  apply to the states . [ 20 ]  In  Rochin , the Court held that evidence obtained in a manner that "shocks the conscience" must be excluded in criminal prosecutions but the court declined to incorporate a broad exclusionary rule for all Fourth Amendment violations. [ 21 ]  By the middle of the twentieth century, many state courts had crafted their own exclusionary rules. [ 22 ]  In 1955, the  California Supreme Court  ruled in  People v. Cahan  that the Fourth Amendment's exclusionary rule applied in California because it was necessary to deter constitutional violations by law enforcement. [ 23 ]  In 1961, the Supreme Court of the United States relied upon  Cahan  to hold in  Mapp v. Ohio  that the exclusionary rule was incorporated to the states. [ 24 ]


On the night of November 12, 1964, Armando Schmerber and a passenger were driving home after drinking at a tavern and bowling alley in the  San Fernando Valley  region of  Los Angeles, California , when their car skidded off the road and struck a tree. [ 25 ]  Schmerber and his companion were injured in the crash and taken to a hospital for treatment. [ 26 ]  When investigating police officers arrived at the hospital, they asked Schmerber to submit a sample of his blood, but Schmerber refused. [ 27 ]  Although they did not possess a  search warrant , officers instructed attending physicians to take a blood sample from Schmerber. [ 28 ]  The blood sample indicated that Schmerber was intoxicated, and he was placed under arrest. [ 29 ]  The blood sample was ultimately admitted into evidence at trial, and Schmerber was convicted for driving under the influence of intoxicating liquors. [ 30 ]  Schmerber objected to the admissibility of the blood sample, claiming that the police violated his rights to  due process , his right against  self-incrimination , his  right to counsel , and his right not to be subjected to  unreasonable searches and seizures . [ 29 ]  The Appellate Department of the California Superior Court rejected Schmerber's arguments, and the California District Court of Appeal declined to review his case. [ fn 2 ] [ 32 ]


"I think it follows if this Court holds that it's proper to withdraw the blood that is certainly just as proper to inject the  Nalline  if we're looking at the welfare of society and how we want to keep  narcotic  users off the street."


Schmerber submitted an appeal to the Supreme Court of the United States, which granted certiorari on January 17, 1966. [ 34 ]  In his brief, Schmerber argued,  inter alia , that the warrantless blood test violated his Fourth Amendment right to be free from unlawful searches and seizures, as well as his Fifth Amendment right against self-incrimination. [ fn 3 ] [ 35 ]  The  Los Angeles City Attorney 's office represented the State of California on appeal. [ 36 ]  In their brief, the City Attorney argued that the blood test did not violate the Fourth Amendment because the seizure was conducted  incident to a lawful arrest . [ 36 ]  The City Attorney also argued that admitting the sample into evidence did not violate Schmerber's Fifth Amendment right against self-incrimination because blood is not testimonial evidence under the Fifth Amendment. [ 36 ]  Oral arguments were held on April 25, 1966, and the Court issued its opinion on June 20, 1966. [ 33 ]


In his majority opinion,  Justice   William J. Brennan, Jr.  held that Schmerber's constitutional rights were not violated when police took his blood without his consent. Relying upon the Court's holding in  Breithaupt v. Abram , he concluded that the police did not violate Schmerber's Fifth Amendment right against self-incrimination because the extraction and chemical analysis of the blood sample did not involve "even a shadow of testimonial compulsion." [ 38 ]  Likewise, Justice Brennan held that the officers did not violate Schmerber's Fourth Amendment right against unreasonable seizures. Justice Brennan wrote that absent exigent circumstances, searches that involve intrusions into the human body require a search warrant. [ 6 ]  Here, the search was not justified as a search incident to arrest because weapons and contraband are not ordinarily concealed beneath the skin. [ 39 ]  However, the involuntary blood draw was justified under the Fourth Amendment's exigent circumstances exception because if the officers had waited to receive a search warrant, evidence of intoxication would have been lost through the body's natural metabolism of alcohol in the bloodstream. [ 40 ]  He wrote that the responding officer "might reasonably have believed that he was confronted with an emergency," where evidence would be destroyed if he waited to receive a warrant. [ 6 ]  Additionally, Justice Brennan cautioned that the Court's ruling was limited "only to the facts of the present record" and that "minor intrusions into an individual's body under stringently limited conditions in no way indicates that it permits more substantial intrusions, or intrusions under other conditions." [ 41 ]


In his concurring opinion, Justice  John Marshall Harlan II  agreed that the involuntary blood sample did not implicate involuntary testimonial compulsion, but wrote separately to emphasize his opinion that the case before the Court "in no way implicates the Fifth Amendment." [ 42 ]  Additionally, Justice Harlan cited to his dissent in  Miranda v. Arizona  where he argued against a broad expansion of the Fifth Amendment right against self-incrimination. Justice Harlan disagreed with the Court's ruling in  Miranda  and even stated that the case "represents poor constitutional law and entails harmful consequences for the country at large." [ 43 ]


All four dissenting Justices wrote separate dissenting opinions in  Schmerber .  Chief Justice   Earl Warren  reiterated his dissenting opinion in  Breithaupt v. Abram , where he argued that involuntary blood samples violate substantive due process. [ 45 ]  Justice  Hugo Black  authored an impassioned dissent in which he argued that the officers violated Schmerber's right against self-incrimination. [ 46 ]  He wrote, "[b]elieving with the Framers that these constitutional safeguards broadly construed by independent tribunals of justice provide our best hope for keeping our people free from governmental oppression, I deeply regret the Court's holding." [ 46 ]  Justice  William O. Douglas  also reiterated his dissent in  Breithaupt v. Abram , but added that physical invasions into the human body violate the right to privacy enumerated in  Griswold v. Connecticut  and that "[n]o clearer invasion of this right of privacy can be imagined than forcible bloodletting of the kind involved here." [ 44 ]  Finally, Justice  Abe Fortas  wrote that the involuntary blood sample was an act of violence that violated substantive due process and that states may not resort to acts of violence when prosecuting crimes. [ 47 ]


In the 1970s and 1980s, the Supreme Court revisited questions about the constitutionality of involuntary bodily intrusions in several key cases. In 1973, the Court ruled in  Cupp v. Murphy  that the police were permitted to extract a tissue sample from underneath a suspect's fingernails to recover "evanescent" physical evidence. [ 48 ]  The suspect in  Cupp  was suspected of strangling his wife and voluntarily went to a police station to answer questions. [ 49 ]  Officers noticed bloodstains under the suspect's fingernails and detained him, but did not place him under arrest. [ 49 ]  Against the suspect's wishes, the police scraped out a tissue sample from under his fingernails to retrieve the evidence. [ 49 ]  The biological material found under the suspect's fingernails was later found to have come from the victim. [ 49 ]  Citing  Schmerber , the Court held that this warrantless search was justified under the exigent circumstances exemption of the Fourth Amendment because the search was necessary to preserve the “highly evanescent evidence” under the defendant's fingernails. [ 50 ]


Twelve years later, the Court again revisited the topic of involuntary bodily intrusions in  Winston v. Lee , where the Court held that the State of  Virginia  could not force an individual to undergo surgery to extract a bullet that may be evidence of a crime. [ 51 ]  The Court applied its previous holding in  Schmerber  to conclude that the surgery would constitute an unreasonable search under the Fourth Amendment and that a crucial factor for evaluating any bodily intrusion "is the extent to which the procedure may threaten the safety or health of the individual." [ 52 ]  Writing for the Court's majority, Justice Brennan concluded that forcing a patient to undergo major surgery intrudes too far upon individual privacy rights and that surgical intrusions "can only be characterized as severe." [ 53 ]


In 1989, the Court ruled in  Skinner v. Railway Labor Executives’ Association  that warrantless blood tests of railroad employees were reasonable under the Fourth Amendment. [ 54 ]  The Court reaffirmed that the “compelled intrusio[n] into the body for blood to be analyzed for alcohol content” is a search under the Fourth Amendment, [ 55 ]  but that warrantless blood tests of railroad employees were necessary to "prevent accidents and casualties in railroad operations that result from impairment of employees by alcohol or drugs.” [ 56 ]  The Court also concluded that when individuals “participate in an industry that is regulated pervasively to ensure safety,” these individuals “have a reduced expectation of privacy.” [ 57 ]  Because these employees had a "diminished expectation of privacy," the warrantless blood tests were permissible. [ 58 ]  Justice  Thurgood Marshall  and Justice Brennan wrote a dissenting opinion in which they argued that this case was distinguishable from  Schmerber  because "no such exigency prevents railroad officials from securing a warrant before chemically testing the samples they obtain." [ 59 ]


After the Court issued its decision in  Schmerber , a split of authority emerged in lower courts with regard to whether the Fifth Amendment's right against self-incrimination prohibited the use of a suspect's refusal to submit to a blood test as evidence of guilt. [ 61 ]  The United States Supreme Court resolved this split in authority in  South Dakota v. Neville , where the Court held that prosecutors could use a suspect's refusal to submit to a blood test as evidence of guilt, and the introduction of this evidence at trial does not violate the suspect's Fifth Amendment right against self-incrimination. [ 62 ]  Writing for the Court's majority, Justice  Sandra Day O'Connor  concluded that "the state did not directly compel respondent to refuse the test" and that a "simple blood-alcohol test is so safe, painless, and commonplace" a suspect would not feel coerced to refuse the test. [ 63 ]  Justice  John Paul Stevens  wrote a dissenting opinion, joined by Justice  Thurgood Marshall , in which he argued that the Court in  Schmerber  intended to adopt a broad and liberal interpretation of the Fifth Amendment right against self-incrimination. [ 64 ]


Over time, a split of authority grew among lower courts with regard to whether the Fourth Amendment's exigent circumstances exception allowed officers to  always  conduct warrantless blood tests on individuals suspected of driving under the influence of alcohol because evidence of alcohol was being destroyed by the body's natural metabolic processes. [ 65 ]  States that recognized this  per se  exigency argued that "[o]nce police arrest a suspect for drunk driving, each passing minute eliminates probative evidence of the crime." [ 66 ]  In 2012, the Court granted review in  Missouri v. McNeely  to resolve this question. [ 67 ]  In a 5–4 opinion, the Court rejected the theory that the natural dissipation of blood alcohol constituted a  per se  exigency. [ 68 ]  Instead, the court affirmed the basic principle from  Schmerber  that absent "an emergency that justifie[s] acting without a warrant," police may not conduct warrantless blood testing on suspects. [ 69 ]  Consequently, exigency in drunk driving cases "must be determined case by case based on the  totality of the circumstances ." [ 70 ]


Scholars have described  Schmerber v. California  as a  landmark case [ 71 ]  and a "watershed moment" in the history of Fourth Amendment jurisprudence. [ 72 ]  Likewise, John D. Castiglione described the case as "seminal for its place in the annals of Fifth Amendment jurisprudence." [ 73 ]  Constitutional law scholar  Akhil Reed Amar  identified  Schmerber  as a turning point in the Fifth Amendment's "distinction between words and physical evidence." [ 74 ]  Anne Marie Schubert has also argued that  Schmerber  served as the genesis for a long line of Supreme Court cases ordering the compelled production of physical evidence. [ 75 ]  Because  Schmerber  foreclosed the use of warrantless blood tests in most circumstances, some scholars, including John A. Scanlan, argue that the Court's ruling was responsible for the proliferation of  breathalyzers  to test for alcohol and  urine analysis  to test for controlled substances in criminal investigations. [ 11 ]


Soon after the Court's ruling, analysts predicted that the effects of the case would be "far-reaching." [ 76 ]  Some analysts feared the ruling would be used to justify "other intrusive searches." [ 77 ]  Other commentators also observed that the Court's holding in  Schmerber  seemed to "reverse direction" from the court's decision in  Miranda v. Arizona  one week earlier, where the Court enlarged protections against the police for criminal suspects. [ 78 ]  However, in his assessment of  Schmerber , Charles L. Berry praised the decision as a "successful effort to find a practical solution to the problem of the drinking motorist." [ 79 ]  Additionally, many  law journals  also offered commentary of the case's significance. For example, a November 1966 article in the  Harvard Law Review  opined that Justice Brennan's majority opinion was "a good exposition of his view of the interrelationship between the fourth and fifth amendments," [ 80 ]  and a February 1967 article in the  Texas Law Review  argued that  Schmerber  "exemplifies the proposition that the fifth amendment is not absolute." [ 81 ]


Some legal scholars have criticized the Court's ruling in Schmerber for infringing too far upon  civil liberty  and privacy. [ 82 ]  E. John Wherry, Jr., former Dean of the  University of Orlando School of Law , wrote that "[b]lindly following  Schmerber  as authorization for all non-consensual blood seizure for forensic purposes is, in this day and age, an outrage." [ 83 ]  Writing for the  Notre Dame Law Review , Blake A. Bailey, Elaine M. Martin, and Jeffrey M. Thompson observed that although the Court limited the holding in  Schmerber  to the facts of the case, prior to  Winston v. Lee , many lower courts relied upon the ruling to order criminal defendants to undergo surgery to remove bullets that may have been evidence of a crime. [ 84 ]  Other scholars have expressed concern that the Court's decision to exclude physical evidence from protections against self-incrimination may one day lead to the use of  mind reading  devices when prosecuting criminal suspects. [ 85 ]  For example, the  Harvard Law Review  suggested that the Court's decision may be used to justify monitoring brain waves. [ 86 ]  Additionally, in an article in the journal  Developments in Mental Health Law , Benjamin Holley suggested that "neurotechnological lie detection" could be used in criminal prosecutions, as long as a suspect's words are not "linked with the physical manifestations sought to be introduced at trial." [ 87 ]  Likewise, in an article in the  Journal of Legal Medicine , John G. New suggested that non-testimonial evidence gathered from  electroencephalography  or  magnetic resonance imaging  may be admissible to demonstrate a suspect's thoughts. [ 88 ]


The citations in this Article are written in  Bluebook  style.


The  Schumm test   (shoom)  is a blood test that uses  spectroscopy  to determine significant levels of  methemalbumin  in the  blood . A positive result could indicate intravascular  hemolysis . [ 1 ] [ 2 ]  The Schumm test was named for  Otto Schumm , a German chemist who lived in the early 20th century. [ citation needed ]


A positive test result occurs when the  haptoglobin  binding capacity of the blood is saturated, leading to heme released from cell free  hemoglobin  to bind to  albumin . [ citation needed ]


Serology  is the scientific study of  serum  and other  body fluids . In practice, the term usually refers to the  diagnostic  identification of  antibodies  in the serum. [ 1 ]  Such antibodies are typically formed in response to an infection (against a given  microorganism ), [ 2 ]  against other foreign proteins (in response, for example, to a  mismatched   blood transfusion ), or to one's own proteins (in instances of  autoimmune disease ). In either case, the procedure is simple. [ citation needed ]


Serological tests are diagnostic methods that are used to identify antibodies and  antigens  in a patient's sample. Serological tests may be performed to diagnose  infections  and  autoimmune illnesses , to check if a person has  immunity  to certain diseases, and in many other situations, such as determining an individual's  blood type . [ 1 ]  Serological tests may also be used in  forensic serology  to investigate crime scene evidence. [ 3 ]  Several methods can be used to detect antibodies and antigens, including  ELISA , [ 4 ]   agglutination ,  precipitation ,  complement-fixation , and  fluorescent antibodies  and more recently  chemiluminescence . [ 5 ]


In  microbiology ,  serologic tests  are used to determine if a person has antibodies against a specific  pathogen , or to detect antigens associated with a pathogen in a person's sample. [ 6 ]   Serologic tests are especially useful for organisms that are difficult to  culture  by routine laboratory methods, like  Treponema pallidum  (the causative agent of  syphilis ), or  viruses . [ 7 ]


The presence of antibodies against a pathogen in a person's blood indicates that they have been exposed to that pathogen. Most serologic tests measure one of two types of antibodies:  immunoglobulin M  (IgM) and  immunoglobulin G  (IgG). IgM is produced in high quantities shortly after a person is exposed to the pathogen, and production declines quickly thereafter. IgG is also produced on the first exposure, but not as quickly as IgM. On subsequent exposures, the antibodies produced are primarily IgG, and they remain in circulation for a prolonged period of time. [ 6 ]


This affects the interpretation of serology results: a positive result for IgM suggests that a person is currently or recently infected, while a positive result for IgG and negative result for IgM suggests that the person may have been infected or immunized in the past. Antibody testing for infectious diseases is often done in two phases: during the initial illness (acute phase) and after recovery (convalescent phase). The amount of antibody in each specimen ( antibody titer ) is compared, and a significantly higher amount of IgG in the convalescent specimen suggests infection as opposed to previous exposure. [ 8 ]  False negative results for antibody testing can occur in people who are  immunosuppressed , as they produce lower amounts of antibodies, and in people who receive  antimicrobial drugs  early in the course of the infection. [ 7 ]


Blood typing  is typically performed using serologic methods. The antigens on a person's red blood cells, which determine their  blood type , are identified using  reagents  that contain antibodies, called  antisera . When the antibodies bind to red blood cells that express the corresponding antigen, they cause red blood cells to clump together (agglutinate), which can be identified visually. The person's blood group antibodies can also be identified by adding plasma to cells that express the corresponding antigen and observing the agglutination reactions. [ 9 ] [ 6 ]


Other serologic methods used in  transfusion medicine  include  crossmatching  and the direct and indirect  antiglobulin tests . Crossmatching is performed before a  blood transfusion  to ensure that the donor blood is compatible. It involves adding the recipient's plasma to the donor blood cells and observing for agglutination reactions. [ 9 ]  The direct antiglobulin test is performed to detect if antibodies are bound to red blood cells inside the person's body, which is abnormal and can occur in conditions like  autoimmune hemolytic anemia ,  hemolytic disease of the newborn  and  transfusion reactions . [ 10 ]   The indirect antiglobulin test is used to screen for antibodies that could cause transfusion reactions and identify certain blood group antigens. [ 11 ]


Serologic tests can help to diagnose autoimmune disorders by identifying abnormal antibodies directed against a person's own tissues ( autoantibodies ). [ 12 ]  All people have different immunology graphs. [ citation needed ]


A 2016 research paper by Metcalf et al., amongst whom were  Neil Ferguson  and  Jeremy Farrar , stated that serological surveys are often used by  epidemiologists  to determine the prevalence of a disease in a population. Such surveys are sometimes performed by random, anonymous sampling from samples taken for other medical tests or to assess the prevalence of antibodies of a specific organism or protective titre of antibodies in a population. Serological surveys are usually used to quantify the proportion of people or animals in a population positive for a specific antibody or the titre or concentrations of an antibody. These surveys are potentially the most direct and informative technique available to infer the dynamics of a population's susceptibility and level of immunity. The authors proposed a  World Serology Bank  (or serum bank) and foresaw "associated major methodological developments in serological testing,  study design , and  quantitative analysis , which could drive a  step change  in our understanding and  optimum control  of  infectious diseases ." [ 13 ]


In a helpful reply entitled "Opportunities and challenges of a World Serum Bank", de Lusignan and Correa observed [ 14 ]  that the


principal  ethical  and logistical challenges that need to be overcome are the methods of obtaining specimens, how  informed consent  is acquired in busy practices, and the filling in of gaps in  patient sampling .


In another helpful reply on the World Serum Bank, the Australian researcher  Karen Coates  declared that: [ 15 ]


Improved serological surveillance would allow  governments ,  aid agencies , and  policy writers  to direct  public health  resources to where they are needed most. A better understanding of  infection dynamics  with respect to the  changing patterns of global weather  should inform policy measures including where to concentrate  vaccination  efforts and  insect control  measures.


In April 2020,  Justin Trudeau  formed the  COVID-19 Immunity Task Force , whose mandate is to carry out a serological survey in a scheme hatched in the midst of the  COVID-19 pandemic . [ 16 ] [ 17 ]


Free light chains (FLCs)  are immunoglobulin light chains that are found in the serum (blood) in an unbound (free) state. In recent decades, measuring the amount of free light chains (FLCs) in the blood has become a practical clinical test. FLC tests can be used to diagnose and monitor diseases like  multiple myeloma  and  amyloidosis .


Each immunoglobulin light-chain molecule contains approximately 220 amino acids in a single polypeptide chain that is folded to form constant and variable region domains.
Each domain comprises two  β-pleated sheets . The sheets are linked by a disulfide bridge and together form a roughly barrel-shaped structure known as a  β-barrel .
The variable (V) domain of light chains has a high degree of structural diversity, particularly the antigen-binding region. In addition, the first 23 amino acids of the 1st variable domain framework region have a number of variations known as subgroups. Four kappa (Vκ1–Vκ4) and six lambda subgroups (Vλ1–Vλ6) can be identified. [ 1 ]  The subgroup structures of FLCs influence their ability to polymerize (combine) and form proteins like amyloid fibrils. For example, the Vλ6 subgroup of FLCs is associated with a type of amyloidosis called AL amyloidosis, while the Vκ1 and Vκ4 subgroups are associated with a different type of amyloidosis called light-chain deposition disease. [ 2 ]


Kappa light-chain molecules are constructed from approximately 40 functional Vκ gene segments (chromosome 2), five Jκ gene segments and a single Cκ gene. Lambda molecules (chromosome 22) are constructed from about 30 Vλ gene segments and four pairs of functional Jλ gene segments and a Cλ gene. [ 3 ]


Light chains are incorporated into immunoglobulin molecules during  B-cell  development and are expressed initially on the surface of pre B-cells. Production of light chains occurs throughout the rest of B-cell development and in plasma cells, where secretion is highest. [ 2 ]


The production of free immunoglobulin light chains in normal individuals is approximately 500 mg/day from bone marrow and lymph node cells. [ 1 ] [ 4 ]  The production of immunoglobulin light chains is about 40% greater than the production of immunoglobulin heavy chains. This may simply be to allow for the proper structure of the intact immunoglobulin molecules, but it is also possible that free light chains have an immunological function. [ 5 ]  There are approximately twice as many kappa-producing plasma cells as lambda plasma cells. Kappa free-light chains are normally monomeric, while lambda free-light chains tend to be dimeric, joined by disulphide bonds. Polymeric forms of both types of free light chain can also occur. [ 6 ]


In normal individuals, free light chains are rapidly cleared from the blood and catabolised by the kidneys. Monomeric free light chains are cleared in 2–4 hours, and dimeric light chains in 3–6 hours. [ 7 ]  Removal may be prolonged to 2–3 days in people with complete renal failure. [ 1 ] [ 4 ] [ 8 ]  Human kidneys are composed of approximately half a million  nephrons . Each nephron contains a  glomerulus  with  basement membrane  pores that allow filtration of immunoglobulin light chains and other small molecules from the blood into the  proximal tubule  of the nephron. [ 1 ]


Filtered molecules are either excreted in the urine or may be specifically re-absorbed. Protein molecules that pass through the glomerular pores are either absorbed unchanged (such as  albumin ), degraded in the proximal tubular cells and absorbed (such as free light chains), or excreted as fragments. [ 9 ]  This re-absorption is mediated by a receptor complex ( megalin / cubulin ) and prevents the loss of large amounts of protein into the urine. It is very efficient and can process 10–30 g of low-molecular-weight proteins per day, so under normal conditions no light chains pass beyond the proximal tubules. [ 10 ] [ 11 ] [ 12 ]


If immunoglobulin light chains are produced in sufficient amounts to overwhelm the proximal tubules' absorption mechanisms (usually due to the presence of a plasma cell tumour) the light chains enter the distal tubules and can appear in the urine ( Bence Jones protein ). The passage of large amounts of immunoglobulin light chains through the kidneys may cause inflammation or blockage of the kidney tubules. [ 2 ]


The  distal tubules  of the kidneys secrete large amounts of uromucoid ( Tamm–Horsfall protein ). This is the dominant protein in normal urine and is thought to be important in preventing ascending urinary infections. It is a relatively small glycoprotein (80 kDa) that aggregates into  polymers  of 20–30 molecules. It contains a short amino-acid sequence that can specifically bind to some free light chains. [ 13 ]  Together they can form an insoluble precipitate which blocks the distal part of the nephrons. This is termed " cast nephropathy " or "myeloma kidney" and is typically found in patients with multiple myeloma. [ 14 ] [ 15 ]  This can block the flow of urine causing the death of the respective nephrons. Rising concentrations of light chains are filtered by the remaining nephrons leading to a cycle of accelerating renal damage with rising concentrations of free light chains in the blood. [ 16 ]  At the same time, the amount of free light chains entering the urine will be decreased and will be zero if the patient stops producing urine ( anuria ). Conversely, urine concentrations of free light chains could increase if renal function improved in a multiple myeloma patient receiving treatment. This could account for the poor correlation frequently seen when urine and serum free light-chain concentrations are compared. [ 17 ] [ 18 ] [ 19 ] [ 20 ]


The 500 mg of FLCs produced per day by the normal  lymphoid system , however, flows through the glomeruli and is completely processed by the proximal tubules. If the proximal tubules of the nephrons are damaged or stressed (such as in hard exercise), filtered FLCs may not be completely metabolised and small amounts may then appear in the urine. [ 9 ]


Serum free light-chain assays have been used in a number of published studies which have indicated superiority over the urine tests, particularly for patients producing low levels of monoclonal free light chains, as seen in nonsecretory multiple myeloma [ 21 ] [ 22 ] [ 23 ]  and AL amyloidosis. [ 23 ] [ 24 ] [ 25 ] [ 26 ]  This is primarily because of the re-absorption of free light chains in the kidneys, creating a threshold of light chain production which must be exceeded before measurable quantities overflow into the urine. [ 17 ] [ 18 ] [ 19 ]  While there are a number of publications indicating that serum free light chain analysis is preferable to urine analysis at diagnosis, [ 27 ] [ 28 ] [ 29 ] [ 30 ]  there is currently no consensus on whether urine tests for monitoring should be replaced. [ 18 ] [ 19 ] [ 20 ] [ 31 ]


A series of studies, principally from the  Mayo Clinic , have indicated that patients with an abnormal free kappa to free lambda ratio have an increased risk of progression to active myeloma from precursor conditions including  monoclonal gammopathy of undetermined significance  (MGUS), [ 32 ] [ 33 ]   smouldering myeloma [ 34 ]  and solitary  plasmacytoma  of the bone. [ 35 ]  Abnormal free light chain production has also been reported to be prognostic of a worse outcome in multiple myeloma [ 36 ] [ 37 ] [ 38 ]  and  chronic lymphocytic leukaemia . [ 39 ]  An abnormal light-chain ratio has been defined as a kappa to lambda chain ratio of less than 0.26 or more than 1.65. [ 32 ]


In 2009, the International Myeloma Working Group published guidelines making recommendations of when serum free light-chain analysis should be used in the management of multiple myeloma. [ 40 ]


The serum free light-chain assay in combination with  serum protein electrophoresis  and serum  immunofixation  electrophoresis is sufficient to screen for pathological monoclonal plasmaproliferative disorders other than AL amyloidosis which requires all the serum tests as well as 24 h urine immunofixation electrophoresis.


Serial serum free light-chain measurement should be routinely performed in patients with AL amyloidosis and multiple myeloma patients with oligosecretory disease.  It should also be done in all patients who have achieved a complete response to treatment to determine whether they have attained a stringent complete response. [ 41 ]


Other guidelines for the use of serum free light chain measurement in the management of AL amyloidosis, [ 42 ]  plasmacytoma [ 43 ]  and the comparison of treatment responses in clinical trials [ 44 ]  have also been published.


Technical and clinical reviews of serum free light-chain measurement have recently been written by Pratt and Jagannath. [ 45 ] [ 46 ]


Serum  iron  is a  medical  laboratory test that measures the amount of circulating  iron  that is bound to  transferrin  and freely circulate in the blood. Clinicians order this laboratory test when they are concerned about  iron deficiency , which can cause  anemia  and other problems. 65% of the iron in the body is bound up in  hemoglobin  molecules in  red blood cells . About 4% is bound up in  myoglobin  molecules. Around 30% of the iron in the body is stored as  ferritin  or  hemosiderin  in the  spleen , the  bone marrow  and the  liver . Small amounts of iron can be found in other molecules in cells throughout the body. None of this iron is directly accessible by testing the serum. [ citation needed ] }


However, some iron is circulating in the serum. Transferrin is a molecule produced by the liver that binds one or two iron(III)  ions , i.e. ferric iron, Fe 3+ ; transferrin is essential if stored iron is to be moved and used. Most of the time, about 30% of the available sites on the transferrin molecule are filled. The test for serum iron uses blood drawn from  veins  to measure the iron ions that are bound to transferrin and circulating in the blood. This test should be done after 12 hours of fasting. The extent to which sites on transferrin molecules are filled by iron ions can be another helpful clinical indicator, known as  percent transferrin saturation . Another lab test saturates the sample to measure the total amount of transferrin; this test is called  total iron-binding capacity  (TIBC). These three tests are generally done at the same time, and taken together are an important part of the diagnostic process for conditions such as  anemia ,  iron deficiency anemia ,  anemia of chronic disease  and  haemochromatosis . [ citation needed ]


Normal  reference ranges  are:


μg/dL =  micrograms  per  deciliter .


Laboratories often use different units and "normal" may vary by population and the lab techniques used; look at the individual laboratory  reference values  to interpret a specific test (for instance, your own).


Serum total protein , also known as  total protein , is a  clinical chemistry   parameter  representing the concentration of  protein  in  serum . [ 1 ]
Serum contains many proteins including  serum albumin , a variety of  globulins , and many others. While it is possible to analyze these proteins individually, total protein is a relatively quick and inexpensive analysis that does not discriminate by protein type.


The traditional method for measuring total protein uses the  biuret reagent , but other chemical methods such as dye-binding and  refractometry  are now available. The measurement is usually performed on  automated analysers  along with other  laboratory  tests. [ citation needed ]


The  reference range  for total protein is typically 60-80g/L. (It is also sometimes reported as "6.0-8.0g/dl"), [ 2 ]  but this may vary depending on the method of analysis.


Serum vitamin B 12   is a  medical  laboratory test that measure  vitamin B 12  only in the  blood  binding to both  transcobalamins . [ 1 ]  Most of the time, 80–94% of vitamin B 12  in the blood binds to  haptocorrin , while only 6–20% is binds to transcobalamin ll. [ 2 ]  Only transcobalamin ll is "active" and can be used by the body. [ 1 ]  Normal total body vitamin B 12  is between 2 and 5 mg with 50% of that stored in the  liver . [ 3 ]  Total serum vitamin B 12  may not be a reliable  biomarker  for reflecting what the body stores inside cells. [ 1 ]  Vitamin B 12  levels can be falsely high or low and data for  sensitivity and specificity  vary widely. There is no gold standard human assay to confirm a  vitamin B 12  deficiency . [ 4 ]


Healthcare providers use this test when a vitamin B 12  deficiency is suspected, which can cause  anemia  and irreversible nerve damage. [ 3 ]  The cutoff between normal vitamin B 12  levels and deficiency varies by country and region. [ 3 ]  A diagnosis of vitamin B 12  deficiency is determined by blood levels lower than 200 or 250  picograms  per ml (148 or 185 picomoles per liter). [ 3 ]  Some people can have symptoms with their normal levels of the vitamin, or may have low levels despite having no symptoms. [ 5 ]  Other tests may be done to ensure individuals status. [ 3 ]  Measuring vitamin B 12  values in individuals during or after treatment, in order to measure the effectiveness of treatment, is useless. [ 6 ]


A blood test shows vitamin B 12  levels in the blood. [ 3 ]  Vitamin B 12  deficiency can be determined, but not always. [ 4 ]  This means it measures forms of vitamin B 12  that are "active" and can be used by the body, as well as the "inactive" forms, which cannot. [ 7 ]  However, also normal or supraphysiological vitamin B 12  levels should be carefully assessed in the context of the individual state of health. [ 1 ]  Elevated or normal serum vitamin B 12  levels may also be associated with a functional vitamin deficiency. [ 1 ]   Functional deficiency has been described despite high B 12  concentrations and is due to a failure of cellular uptake, intracellular processing, trafficking, or utilization. [ 1 ]  However, low vitamin B 12  levels may occur other than the true deficiency for various reasons and circumstances. [ 8 ]  High or supraphysiological serum levels are usually not of concern, although without supplementation they have been associated with many pathological conditions. [ 1 ]


Laboratories often use different units and "normal" may vary by population and the lab techniques used. Some researchers have suggested that current standards for vitamin B 12  levels are too low. [ 9 ]


The  ST Genesia  is a  fully automated  commercial analyzer system for performing  thrombin generation assays  (TGAs) and hence for  coagulation testing . [ 1 ]  It was developed by Diagnostica Stago and was introduced by the company in 2018. [ 2 ]


Traditionally, TGAs has been conducted using partially automated methods like the  calibrated automated thrombogram  (CAT), which was introduced in 2003. [ 1 ] [ 3 ] [ 4 ]  However, the CAT is performed in a  96-well plate  and requires specialized  technologists  to be performed. [ 1 ]  Consequently, it has seen low implementation in routine laboratories and has been more limited to research settings. [ 1 ] [ 5 ]  Lack of  standardization  with the CAT has also led to difficulties in study-to-study comparisons in research. [ 1 ] [ 6 ]  It has been said that the introduction of the ST Genesia system, which will allow TGAs to be performed more easily and also shows improved  reproducibility  compared to the CAT, should allow for more widespread adoption of TGAs in clinical laboratories. [ 1 ] [ 7 ]


The  Staub-Traugott Phenomenon  (or Staub-Traugott Effect) is the premise that a normal subject fed  glucose  will rapidly return to normal levels of  blood glucose  after an initial spike, and will see improved reaction to subsequent glucose feedings. [ citation needed ]


A. T. B. Jacobson determined in 1913 that  carbohydrate  ingestion results in blood glucose fluctuations. [ 1 ]  Hamman and Hirschman first reported improvement of carbohydrate tolerance following repeated glucose administration in 1919. [ 2 ]  H. Staub in 1921 and K. Traugott in 1922 subsequently confirmed the improved reaction in healthy subjects and the phenomenon was named for them. [ 3 ] [ 4 ]  As this effect does not occur in  diabetic  subjects, it became the basis for the  Glucose Tolerance Test . [ citation needed ]


Abraira and Lawrence describe the original discovery as being that "when glucose loads are given in succession, orally or intravenously, significant and progressive improvement in glucose tolerance will occur in normal and nonketotic diabetic subjects. This facilitated disposal of a glucose load is known as the Staub-Traugott phenomenon." [ 5 ]


This phenomenon drew considerable interest as it was demonstrated that the ingested glucose was still being processed by the gut at the same rate while being cleared much more rapidly in the bloodstream. "It is not surprising that when a large amount of readily diffusible glucose is suddenly introduced into the alimentary tract the rate of absorption should exceed the rate at which the tissues can abstract it from the blood. But it is not so clear why the curve should again fall to normal as rapidly as it often does at a time when the rate of absorption from the gut can be scarcely diminished." [ 6 ]


Various mechanisms were hypothesized involving the  liver  and  insulin . It was determined in 2009 that "enhanced potentiation of insulin response and increased suppression of hepatic glucose production are the main mechanisms underlying the Staub-Traugott effect", meaning that the liver slows its release of glucose into the bloodstream and the existing insulin becomes better at clearing glucose from the bloodstream with each dose of glucose administered. [ 7 ]


This effect has been observed to disappear under conditions of  starvation  and in  hypopituitary  patients. [ 5 ] [ 8 ]


Attempts to base dietary and nutrition advice on this effect have met with limited success. [ 9 ]


The  sum activity of peripheral deiodinases  ( G D , also referred to as  deiodination capacity ,  total deiodinase activity  or, if calculated from levels of thyroid hormones, as  SPINA-GD [ a ] ) is the maximum amount of  triiodothyronine  produced per time-unit under conditions of substrate saturation. [ 1 ]  It is assumed to reflect the activity of  deiodinases  outside the  central nervous system  and other isolated compartments. GD is therefore expected to reflect predominantly the activity of  type I deiodinase .


G D  can be determined experimentally by exposing a  cell culture  system to saturating concentrations of  T4  and measuring the  T3  production. Whole body deiodination activity can be assessed by measuring production of radioactive iodine after loading the organism with marked thyroxine. [ 2 ]


However, both approaches are faced with draw-backs. Measuring deiodination in cell culture delivers little, if any, information on total deiodination activity. Using marked thyroxine exposes the body to  thyrotoxicosis  and radioactivity. Additionally, it is not possible to differentiate step-up reactions resulting in T3 production from the step-down reaction catalyzed by type 3 deiodination, which mediates production of  reverse T3 . Distinguishing the contribution of distinct deiodinases is possible, however, by sequential approaches using deiodinase-specific blocking agents, but this approach is cumbersome and time-consuming. [ 2 ]


In vivo , it may therefore be beneficial to estimate  G D  from equilibrium levels of T4 and T3. It is obtained with


G
 ^

 D

 =

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 31

 (

 K

 M
 1

 +
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 T

 4

 ]
 )
 (
 1
 +

 K

 30

 [
 T
 B
 G
 ]
 )
 [
 F

 T

 3

 ]

 α

 31

 [
 F

 T

 4

 ]

 {\displaystyle {\hat {G}}_{D}={{\beta _{31}(K_{M1}+[FT_{4}])(1+K_{30}[TBG])[FT_{3}]} \over {\alpha _{31}[FT_{4}]}}}


G
 ^

 D

 =

 β

 31

 (

 K

 M
 1

 +
 [
 F

 T

 4

 ]
 )
 [
 T

 T

 3

 ]

 α

 31

 [
 F

 T

 4

 ]

 {\displaystyle {\hat {G}}_{D}={{\beta _{31}(K_{M1}+[FT_{4}])[TT_{3}]} \over {\alpha _{31}[FT_{4}]}}}


[ FT4 ]: Serum free T4 concentration (in pmol/L)
[ FT3 ]: Serum free T3 concentration (in pmol/L)
[ TT3 ]: Serum total T3 concentration (in nmol/L)

 α

 31

 {\displaystyle \alpha _{31}}

 :  Dilution  factor for T3 (reciprocal of apparent volume of distribution, 0.026 L −1 )

 β

 31

 {\displaystyle \beta _{31}}

 :  Clearance  exponent for T3 (8e-6 sec −1 ) (i. e.,  reaction rate constant  for degradation)
 K M 1 :  Binding constant  of type-1-deiodinase (5e-7 mol/L)
 K 30 : Binding constant T3-TBG (2e9 L/mol) [ 3 ]


The method is based on mathematical models of thyroid homeostasis. [ 1 ] [ 3 ]  Calculating deiodinase activity with one of these equations is an  inverse problem . Therefore, certain conditions (e.g. stationarity) have to be fulfilled to deliver a reliable result.


The product of SPINA-GD times the urinary  iodine  excretion can be used to assess iodine-independent factors affecting deiodinase activity, e.g. selenium deficiency. [ 4 ]


The equations and their parameters are calibrated for adult humans with a body mass of 70 kg and a plasma volume of ca. 2.5 L. [ 3 ]


SPINA-GD correlates to the T4-T3 conversion rate in slow tissue pools, as determined with isotope-based measurements in healthy volunteers. [ 1 ]  It was also shown that GD correlates with  resting energy expenditure , [ 5 ]   body mass index [ 3 ] [ 6 ] [ 7 ]  and thyrotropin levels in humans, [ 8 ] [ 9 ]  and that it is reduced in  nonthyroidal illness  with hypodeiodination. [ 6 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ]  Multiple studies demonstrated SPINA-GD to rise after initiation of substitution therapy with  selenium , a trace element that is essential for the synthesis of deiodinases. [ 14 ] [ 15 ] [ 16 ] [ 17 ] [ 18 ]  Conversely, it was observed that SPINA-GD is reduced in persons positive for autoantibodies to  selenoprotein P , which is assumed to be involved in transport and storage of selenium. [ 4 ]


Compared to both healthy volunteers and subjects with  hypothyroidism  and  hyperthyroidism , SPINA-GD is reduced in  subacute thyroiditis . In this condition, it has a higher  specificity ,   positive  and  negative likelihood ratio  than serum concentrations of  thyrotropin , free T4 or free T3. [ 3 ]  These measures of diagnostic utility are also high in nodular  goitre , where SPINA-GD is elevated. [ 3 ]  Among subjects with subclinical thyrotoxicosis, calculated deiodinase activity is significantly lower in  exogenous thyrotoxicosis  (resulting from therapy with levothyroxine) than in true hyperthyroidism (ensuing from  toxic adenoma ,  toxic multinodular goitre  or  Graves' disease ). [ 19 ]  SPINA-GD may therefore be an effective  biomarker  for the differential diagnosis of thyrotoxicosis. [ 20 ] [ 21 ]


Compared to healthy subjects, SPINA-GD is significantly reduced in  euthyroid sick syndrome . [ 22 ]


Recent research revealed total deiodinase activity to be higher in untreated hypothyroid patients as long as thyroid tissue is still present. [ 9 ]  This effect may ensue from the existence of an effective TSH-deiodinase axis or  TSH-T3 shunt . After total  thyroidectomy  or high-dose  radioiodine  therapy (e.g. in treated  thyroid cancer ) as well as after initiation of substitution therapy with levothyroxine the activity of step-up deiodinases decreases [ 23 ] [ 24 ]  and the correlation of SPINA-GD to thyrotropin concentration is lost. [ 25 ]  In patients suffering from toxic adenoma, toxic multinodular goitre and Graves’ disease low-dose  radioiodine therapy  leads to a significant reduction of SPINA-GD as well. [ 26 ]


SPINA-GD is elevated in obesity. This applies to both the metabolically healthy obese (MHO) or metabolically unhealthy obese (MUO) phenotypes. [ 27 ]  In two large population-based cohorts within the  Study of Health in Pomerania  SPINA-GD was positively correlated to some markers of  body composition  including  body mass index  (BMI),  waist circumference , fat-free mass and body cell mass, [ 28 ]  confirming observations in the  NHANES  dataset [ 29 ]  and in a Chinese study. [ 30 ]  This positive association was age-dependent and with respect to BMI significant in young subjects only, but with respect to body cell mass stronger in elderly persons. [ 28 ]  Generally, SPINA-GD seems to be upregulated in  metabolic syndrome , as demonstrated by a significant correlation to the triglyceride-glucose index, a marker of  insulin resistance . [ 31 ]


SPINA-GD is reduced in  low-T3 syndrome [ 32 ]  and certain chronic diseases, e.g.  chronic fatigue syndrome , [ 33 ] [ 4 ]   chronic kidney disease , [ 34 ] [ 35 ]   short bowel syndrome [ 36 ]  or geriatric  asthma . [ 37 ]  Six months after the primary infection, it correlates negatively to the FS-14 score for  fatigue  in patients affected by  Long COVID  (PASC) [ 38 ] . In  Graves' disease , SPINA-GD is initially elevated but decreases with antithyroid treatment in parallel to declining TSH receptor autoantibody titres. [ 5 ]  Although  takotsubo syndrome  (TTS) results in most cases from  psychosocial stressors , thereby reflecting type 2  allostatic load , SPINA-GD has been described to be reduced in TTS. [ 39 ]  This may result from concomitant  non-thyroidal illness syndrome , so that the clinical phenotype represents overlapping type 1 and type 2 allostatic response. In a large register-based study, reduced SPINA-GD predicted a poor outcome of Takotsubo syndrome. [ 40 ]


In certain psychiatric diseases, including major depression, bipolar disorder and schizophrenia SPINA-GD is reduced compared to healthy controls. [ 41 ]  This observation is supported by negative correlation of SPINA-GD with the depression percentiles in the  Hospital Anxiety and Depression Scale  (HADS). [ 42 ]


In hyperthyroid [ 43 ]  men both  SPINA-GT  and SPINA-GD negatively correlate to  erectile function , intercourse satisfaction,  orgasmic function  and  sexual desire . Substitution with  selenomethionine  results in increased SPINA-GD in subjects with autoimmune thyroiditis. [ 14 ] [ 15 ] [ 16 ] [ 17 ]


In subjects with  diabetes mellitus  SPINA-GD is positively correlated to several bone resorption markers including the N-mid fragment of osteocalcin and procollagen type I N-terminal propeptide (P1NP), as well as, however in men only, the β-C-terminal cross-linked telopeptides of type I collagen (β-CTX). [ 44 ]  In the general population it is, however, positively associated with the bone mineral density of the femoral neck and with reduced risk of osteoporosis. [ 45 ]  In both diabetic and non-diabetic subsjects it correlates (negatively) with age and concentrations of  c-reactive protein ,  troponin T  and  B-type natriuretic peptide , and (positively) with the concentrations of total  cholesterol ,  low-density lipoprotein  and  triglycerides . [ 46 ]


Deiodination capacity proved to be an independent predictor of substitution dose in several trials that included persons on replacement therapy with  levothyroxine . [ 47 ] [ 48 ]


Probably as a consequence of  non-thyroidal illness syndrome , SPINA-GD predicts  mortality  in  trauma [ 22 ]  and postoperative  atrial fibrillation  in patients undergoing cardiac surgery. [ 12 ]   The association to mortality is retained even after adjustment for other established risk factors, including age,  APACHE II  score and plasma protein binding of thyroid hormones. [ 22 ]  Correlations were also shown to age, total atrial conduction time, and concentrations of  3,5-diiodothyronine  and  B-type natriuretic peptide . [ 12 ]  SPINA-GD also correlates with several components of the  kynurenine pathway , which might mirror an assosication to a pro-inflammatory milieu. [ 49 ]  Accordingly, in a population suffering from pyogenic liver abscess SPINA-GD correlated to markers of  malnutrition ,  inflammation  and  liver failure . [ 32 ]  A study on subjects with  Parkinson's disease  found SPINA-GD to be significantly decreased in  tremor -dominant and mixed subtypes compared to the akinetic-rigid type. [ 50 ]   Euthyroid sick syndrome  may be the reason for variations of SPINA-GD in subjects treated with  immune checkpoint inhibitors  for  cancer  as well. [ 51 ]