The donor blood undergoes  leukapheresis , a process by which white blood cells are separated from  red blood cells  and  plasma . During the blood collection, the donor's blood is mixed with  hydroxyethyl starch , which helps separate the granulocytes from other blood components during sample processing. [ 2 ] [ 11 ] : 297   The other components of the blood are returned to the donor's circulation. [ 11 ] : 297   The process of collecting the granulocytes takes about four to five hours. [ 2 ]  Because a large amount of blood (seven to ten litres) is processed during apheresis, donors may experience adverse effects from changes in  fluid balance . [ 4 ]  An alternative approach, more commonly used in the United Kingdom, is to combine the  buffy coats  (the fraction of blood containing white blood cells) from multiple routine blood donations to create a blood product containing a high amount of granulocytes. [ 12 ]


Once collected, granulocytes have a 24-hour shelf life. [ 12 ]  It is recommended that they are transfused within a few hours of collection. [ 2 ]  They cannot be frozen, as this severely inhibits the cells' functions. [ 10 ] : 628   The white blood cell concentrate obtained through leukapheresis contains a high number of active  T lymphocytes , which can cause  graft-versus-host disease  in the recipient, so it is often exposed to radiation to inactivate these cells. [ 10 ] : 628


Adverse effects  are more common with granulocyte transfusions than with  red blood cell transfusions . 25 to 50 percent of people who receive granulocyte transfusions experience mild to moderate side effects, while 1 percent experience severe complications. [ 2 ]   Fever  and chills are common side effects. [ 2 ] [ 3 ]  Granulocyte transfusions may affect the  lungs , causing cough,  difficulty breathing ,  low oxygen levels , and abnormal  chest X-rays . [ 2 ]  These lung complications may potentially be fatal. [ 3 ]  A review paper found that the frequency of lung-related side effects ranged from 0 to 53 percent. [ 13 ]


On rare occasions, recipients can develop  transfusion-transmitted diseases  if  pathogens  are present in the donor blood. This is a particular problem with granulocyte transfusions because of their short shelf life, which means they must be transfused before infectious disease testing is complete. [ 2 ]  Infection with  cytomegalovirus  (CMV) is a concern, as this virus is found in white blood cells, so if the recipient is at risk of developing severe disease from CMV, it is recommended that granulocytes be collected from a CMV-negative donor. [ 3 ]


If the donor white blood cells are not irradiated, the recipient may be at risk of developing  graft-versus-host  disease. Finally, people who receive granulocyte transfusions may develop  antibodies  against the  human leukocyte antigens  found on the surface of white blood cells, which can predispose them to transfusion reactions, decrease the lifespan of donor white blood cells in their circulation, and reduce the efficacy of  platelet transfusions  and  allogeneic stem cell transplants . [ 2 ] [ 3 ]


In a 1934 experiment, Strumia gave neutropenic patients  intramuscular injections  of neutrophils, but this proved ineffective in improving their neutrophil function. [ 14 ] [ 15 ]  In 1953, Brecher et al. demonstrated the principle behind granulocyte transfusion by infusing neutrophils into dogs and showing that they travelled to sites of inflammation. [ 16 ]  The first human granulocyte transfusions were carried out in the 1960s, using white blood cells harvested from people with chronic myeloid leukemia and concentrated using  centrifugation . Steroid treatment and leukapheresis were later introduced, allowing granulocytes to be collected from healthy donors. However, these techniques were not very effective as they did not produce a high granulocyte count. Owing to poor efficacy, an undesirable side effect profile, and the impracticality of storing granulocytes for an extended period of time, the use of granulocyte transfusions declined. [ 4 ]  Improvements in antimicrobial therapy and supportive care also played a role in the treatment's decreasing popularity. [ 2 ]  However, the introduction of donor treatment with G-CSF in the 1990s allowed high numbers of granulocytes to be collected from healthy donors. This, combined with an increasing number of people with severe neutropenia as a result of chemotherapy and the growing prevalence of  multidrug resistant infections , led to a renewal of interest in granulocyte transfusions. [ 4 ]


Gulf Coast Regional Blood Center  is an  nonprofit , independent  blood donor  center that gathers blood through donations and provides  whole blood  and  blood products . The center meets the blood and blood component needs of patients being treated in more than 170 health care institutions in a 25-county  Texas   Gulf Coast , Brazos Valley and east Texas regions. [ 1 ]  Located in the  Texas Medical Center  in  Houston , the center began operations on January 1, 1975. The Blood Center encourages individuals to Commit for Life, which is a partnership between the community and Gulf Coast Regional Blood Center that is focused on saving lives and permanently increasing the blood supply. The center is headquartered in  Houston . [ 2 ]


The center stated that, for it to serve its area effectively, it would have to collect 333,000 units in 2010, with more
than 1,000 donations per day. [ 3 ]   Gulf Coast Regional Blood Center is a non-profit  501 (c) (3)  organization and is accredited, licensed and inspected by  American Association of Blood Banks , the  Food and Drug Administration ,  Medicare  as well as local and state authorities. In 2007, the center collected a total of 291,319 units of blood and blood components, exceeding 2006's record by more than 18,000 units. [ 4 ]


The center is an accredited donor center for the  National Marrow Donor Program  and has recruited more than 90,000 potential donors who can donate  bone marrow  or  hematopoietic  cells. [ 5 ]  The center is one of the leading bone-marrow donor centers in the country and is the leading center for minority recruitment according to the National Marrow Donor Program. The center's marrow donor registry has a donor base of more than 100,000 donors, and through 2007, facilitated 329 matches. [ 6 ]


"Commit for Life" refers to the blood center's blood donation programs. Blood donations may be done on an individual basis, on a group basis, or on a volunteer basis. [ 7 ]


This  Houston -related article is a  stub . You can help Wikipedia by  expanding it .


Hemolytic disease of the newborn , also known as  hemolytic disease of the fetus and newborn ,  HDN ,  HDFN , or  erythroblastosis fetalis , [ 1 ] [ 2 ]  is an  alloimmune  condition that develops in a  fetus  at or around birth, when the  IgG  molecules (one of the five main types of  antibodies ) produced by the mother pass through the  placenta . Among these antibodies are some which attack  antigens  on the  red blood cells  in the  fetal circulation ,  breaking down and destroying the cells . The fetus can develop  reticulocytosis  and  anemia . The intensity of this fetal disease ranges from mild to very severe, and fetal death from heart failure ( hydrops fetalis ) can occur. When the disease is moderate or severe, many  erythroblasts  (immature red blood cells) are present in the fetal blood, earning these forms of the disease the name  erythroblastosis fetalis  ( British English :  erythroblastosis foetalis ).


HDFN represents a breach of  immune privilege  for the fetus or some other form of impairment of the  immune tolerance in pregnancy . Various types of HDFN are classified by which alloantigen provokes the response. The types include  ABO ,  anti-RhD ,  anti-RhE ,  anti-Rhc , anti-Rhe, anti-RhC, multiantigen combinations, and  anti-Kell . Although global prevalence studies of the differential contribution of those types are lacking, regional  population studies  have shown the anti-RhD type to be the most common cause of HDFN, followed by anti-RhE, anti-RhC, and anti-Rhc. [ 3 ]


Signs of hemolytic disease of the newborn include a positive  direct Coombs test  (also called direct agglutination test), elevated cord bilirubin levels, and  hemolytic anemia . It is possible for a newborn with this disease to have  neutropenia  and  neonatal alloimmune thrombocytopenia  as well. [ citation needed ]   Hemolysis  leads to elevated  bilirubin  levels. After delivery, bilirubin is no longer cleared (via the placenta) from the neonate's blood and the  symptoms  of  jaundice  (yellowish skin and yellow discoloration of the whites of the eyes, or  icterus ) increase within 24 hours after birth. Like other forms of severe  neonatal jaundice , there is the possibility of the neonate developing acute or chronic  kernicterus , however the risk of kernicterus in HDN is higher because of the rapid and massive destruction of blood cells. Isoimmunization is a risk factor for  neurotoxicity  and lowers the level at which kernicterus can occur. Untreated profound anemia can cause high-output  heart failure , with  pallor ,  enlarged liver  and/or  spleen , generalized  swelling , and  respiratory distress . [ citation needed ]


HDN can be the cause of  hydrops fetalis , an often-severe form of prenatal  heart failure  that causes fetal  edema . [ 5 ]


Complications of HDN could include  kernicterus ,  hepatosplenomegaly , inspissated (thickened or dried) bile syndrome and/or greenish staining of the  teeth ,  hemolytic anemia  and damage to the liver due to excess bilirubin. Conditions that may cause similar symptoms in the newborn period include:  acquired hemolytic anemia , congenital  toxoplasma , congenital  syphilis  infection, congenital obstruction of the  bile duct , and  cytomegalovirus  (CMV) infection. [ citation needed ]


Antibodies are produced when the body is exposed to an  antigen  foreign to the make-up of the body. If a mother is exposed to a foreign antigen and produces IgG (as opposed to  IgM  which does not cross the placenta), the IgG will target the antigen, if present in the fetus, and may affect it  in utero  and persist after delivery. However, the antibodies of the mother do not go away after the first incompatible pregnancy due to immunological memory. The maternal blood is likely to secrete more antibodies and attack the fetal erythrocytes during subsequent pregnancies because of re-exposure to the antigen.  [ 15 ]  The three most common models in which a woman becomes sensitized toward (i.e., produces IgG  antibodies  against) a particular antigen are hemorrhage, blood transfusion, and ABO incompatibility. [ citation needed ]


Fetal-maternal hemorrhage , which is the movement of fetal blood cells across the placenta, can occur during  abortion ,  ectopic pregnancy ,  childbirth , ruptures in the  placenta  during  pregnancy  (often caused by trauma), or medical procedures carried out during pregnancy that breach the uterine wall. In subsequent pregnancies, if there is a similar incompatibility in the fetus, these antibodies are then able to cross the placenta into the fetal bloodstream to attach to the  red blood cells  and cause their destruction ( hemolysis ). This is a major cause of HDN, because 75% of pregnancies result in some contact between fetal and maternal blood, and 15–50% of pregnancies have hemorrhages with the potential for immune sensitization. The amount of fetal blood needed to cause maternal sensitization depends on the individual's immune system and ranges from 0.1 mL to 30 mL. [ 5 ]


The woman may have received a therapeutic  blood transfusion .  ABO blood group system  and the D antigen of the  Rhesus (Rh) blood group system  typing are routine prior to transfusion. Suggestions have been made that women of child-bearing age or young girls should not be given a transfusion with Rhc-positive blood or  Kell 1 -positive blood to avoid possible sensitization, but this would strain the resources of blood transfusion services, and it is currently considered uneconomical to screen for these blood groups. HDFN can also be caused by antibodies to a variety of other  blood group system  antigens, but Kell and Rh are the most frequently encountered. [ citation needed ]


The third sensitization model can occur in women of blood type O. The  immune response  to A and B antigens, which are widespread in the environment, usually leads to the production of IgM or IgG anti-A and anti-B antibodies early in life. Women of blood type O are more prone than women of types A and B to making IgG anti-A and anti-B antibodies, and these IgG antibodies are able to cross the placenta. For unknown reasons, the incidence of maternal antibodies against type A and B antigens of the IgG type that could potentially cause hemolytic disease of the newborn is greater than the observed incidence of "ABO disease." About 15% of pregnancies involve a type O mother and a type A or type B child; only 3% of these pregnancies result in hemolytic disease due to A/B/O incompatibility. In contrast to antibodies to A and B antigens, production of Rhesus antibodies upon exposure to environmental antigens seems to vary significantly across individuals. [ 16 ]  In cases where there is ABO incompatibility and Rh incompatibility, the risk of alloimmunization is decreased because fetal red blood cells are removed from maternal circulation due to anti-ABO antibodies before they can trigger an anti-Rh response. [ 5 ]


HDN is classified by the type of antigens involved. The main types are ABO HDN, Rhesus HDN, Kell HDN, and other antibodies. Combinations of antibodies (for example, anti-Rhc and anti-RhE occurring together) can be especially severe. [ citation needed ]


ABO hemolytic disease of the newborn  can range from mild to severe, but generally, it is a mild disease. It can be caused by anti-A and anti-B antibodies. [ 17 ]


Rhesus D hemolytic disease of the newborn  (often called Rh disease) is the most common and only preventable form of severe HDN. Since the introduction of Rho-D immunoglobulin, ( Rhogam , at 1968, which prevents the production of maternal Rho-D antibodies, the incidence of anti-D HDN has decreased dramatically. [ 5 ] [ 18 ]


Rhesus c HDFN  can range from a mild to severe disease and is the third most common form of severe HDN. [ 19 ]  Rhesus e and rhesus C hemolytic disease of the newborn are rare. Anti-C and anti-c can both show a negative DAT but still have a severely affected infant. [ 20 ] [ 21 ]  An indirect Coombs must also be run.


Anti-Kell hemolytic disease of the newborn  is most commonly caused by anti-K 1  antibodies, the second most common form of severe HDN. Over half of the cases of anti-K 1  related HDN are caused by multiple blood transfusions. Antibodies to the other Kell antigens are rare. [ 19 ]  Anti-Kell can cause severe anemia regardless of titer. [ 22 ]  It suppresses the bone marrow by inhibiting the erythroid progenitor cells. [ 23 ] [ 24 ] [ 25 ]


Anti-M also recommends antigen testing to rule out the presence of HDN as the direct coombs can come back negative in a severely affected infant. [ 26 ]


Kidd antigens are also present on the endothelial cells of the kidneys. [ 27 ] [ 28 ]


One study states that it would be unwise to routinely dismiss anti-E as being of little clinical consequence. It also found that the most severe case of anti-E HDFN occurred with titers 1:2, concluding that titers are not reliable for the diagnosis of the anti-E type. [ 29 ]


The  diagnosis  of HDFN is based on history and laboratory findings. If a newly pregnant woman has red cell antibodies in her serum, the antibody titer should be followed with subsequent blood draws. The titer will rise if the fetus expresses the red cell antigen to which she is alloimmunized. In that case, fetal  middle cerebral artery   doppler ultrasonography  is used to determine the degree of fetal anemia and the need for  intrauterine transfusion . [ 30 ]


Blood tests done on the newborn baby


Blood tests done on the mother


Blood tests done on the father  (rarely needed)


In cases of Rho(D) incompatibility,  Rho(D) immunoglobulin  is given to prevent sensitization. However, there is no comparable immunotherapy available for other blood group incompatibilities. [ 5 ]


Early pregnancy


Mid- to late- pregnancy


Rhesus-negative mothers who are pregnant with a rhesus-positive infant are offered Rho(D) immune  globulin  (RhIG, or RhoGam) at 28 weeks during pregnancy, at 34 weeks, and within 48 hours after delivery to prevent sensitization to the D antigen. It works by binding any fetal red blood cells with the D antigen before the mother is able to produce an immune response and form anti-D IgG. [ 5 ]  A drawback to pre-partum administration of RhIG is that it causes a positive antibody screen when the mother is tested, which can be difficult to distinguish from natural immunological responses that result in antibody production. [ citation needed ]  Without Rho(D) immunoglobulin, the risk of isoimmunization is approximately 17%; with proper administration, the risk is reduced to less than 0.1–0.2%. [ 5 ]


In some cases, the direct Coombs will be negative but severe, even fatal HDN can occur. [ 20 ]  An indirect Coombs needs to be run in cases of anti-C, [ 21 ]  anti-c, [ 21 ]  and anti-M. Infants with Anti-M are also recommended to receive antigen testing to rule out the presence of HDN. [ 26 ]  The below tests are often useful in cases of hemolytic disease of the newborn but are not required for treatment of all newborns.


After birth, treatment depends on the severity of the condition, but could include temperature stabilization and monitoring,  phototherapy , transfusion with compatible packed red blood,  exchange transfusion ,  sodium bicarbonate  for correction of  acidosis  and/or assisted ventilation. [ 43 ]


Once a woman has antibodies, she is at high risk for a future transfusion reaction if she is in need of a blood transfusion. [ 48 ]  For this reason, she is advised to carry a medical alert card at all times and inform all doctors and emergency personnel of her antibody status. [ citation needed ]  The absence of antibodies however does not preclude a woman from having a transfusion reaction:


"Acute hemolytic transfusion reactions may be either immune-mediated or nonimmune-mediated. Immune-mediated hemolytic transfusion reactions caused by immunoglobulin M (IgM) anti-A, anti-B, or anti-A, B typically result in severe, potentially fatal complement-mediated intravascular hemolysis. Immune-mediated hemolytic reactions caused by IgG, Rh, Kell, Duffy, or other non-ABO antibodies typically result in extravascular sequestration, shortened survival of transfused red cells, and relatively mild clinical reactions. Acute hemolytic transfusion reactions due to immune hemolysis may occur in patients who have no antibodies detectable by routine laboratory procedures." [ 49 ]


For a summary of transfusion reactions in the US, see reference. [ 50 ]


In 2003, the incidence of Rh(D) sensitization in the United States was 6.8 per 1000 live births; 0.27% of women with an Rh incompatible fetus experience alloimmunization. [ 5 ]


In  ABO hemolytic disease of the newborn  (also known as ABO HDN) maternal  IgG   antibodies  with specificity for the  ABO blood group system  pass through the  placenta  to the  fetal  circulation where they can cause  hemolysis  of fetal  red blood cells  which can lead to fetal  anemia  and  HDN . In contrast to  Rh disease , about half of the cases of ABO HDN occur in a firstborn baby and ABO HDN does not become more severe after further pregnancies. [ citation needed ]


The ABO blood group system is the best known surface antigen system, expressed on a wide variety of human cells. For  Caucasian  populations about one fifth of all pregnancies have ABO incompatibility between the fetus and the mother, but only a very small minority develop symptomatic ABO HDN. [ 1 ]  The latter typically only occurs in mothers of blood group O, because they can produce enough IgG antibodies to cause hemolysis. [ citation needed ]


Although very uncommon, cases of ABO HDN have been reported in infants born to mothers with blood groups A [ 2 ] [ 3 ]  and B. [ 4 ]


In about a third of all ABO incompatible pregnancies maternal IgG anti-A or IgG anti-B antibodies pass through the placenta to the fetal circulation leading to a weakly positive  direct Coombs test  for the neonate's blood. [ citation needed ]   However, ABO HDN is generally mild and short-lived and only occasionally severe because:


Routine  antenatal  antibody screening blood tests ( indirect Coombs test ) do not screen for ABO HDN. [ citation needed ]   If IgG anti-A or IgG anti-B antibodies are found in the pregnant woman's blood, they are not reported with the test results, because they do not correlate well with ABO HDN. [ citation needed ]   Diagnosis is usually made by investigation of a newborn baby who has developed  jaundice  during the first week of life.


Testing


The antibodies in ABO HDN cause  anemia  due to destruction of fetal red blood cells and  jaundice  due to the rise in blood levels of  bilirubin  a by-product of  hemoglobin  break down. If the anemia is severe, it can be treated with a blood transfusion, however this is rarely needed. On the other hand, neonates have underdeveloped livers that are unable to process large amounts of bilirubin and a poorly developed  blood–brain barrier  that is unable to block bilirubin from entering the brain. This can result in  kernicterus  if left unchecked. If the bilirubin level is sufficiently high as to cause worry, it can be lowered via  phototherapy  in the first instance or an  exchange transfusion  if severely elevated. [ citation needed ]


Hemolytic disease of the newborn (anti-Kell 1 )  is the second most common cause of severe  hemolytic disease of the newborn  (HDN) after  Rh disease . [ 1 ]   Anti-Kell 1  is becoming relatively more important as prevention of Rh disease is also becoming more effective.


Hemolytic  disease of the  newborn  (anti-Kell 1 ) is caused by a mismatch between the  Kell antigens  of the  mother  and  fetus .  About 91% of the population are Kell 1  negative and about 9% are Kell 1  positive.  A fraction of a percentage are  homozygous  for Kell 1 . Therefore, about 4.5% of babies born to a Kell 1  negative mother are Kell 1  positive. [ citation needed ]


The disease results when maternal  antibodies  to Kell 1  are transferred to the fetus across the  placental barrier , breaching  immune privilege . These antibodies can cause severe  anemia  by interfering with the early proliferation of  red blood cells  as well as causing  alloimmune  hemolysis.  Very severe disease can occur as early as 20 weeks gestation.   Hydrops fetalis  can also occur early.  The finding of anti-Kell antibodies in an antenatal screening blood test ( indirect Coombs test ) is an indication for early referral to a specialist service for assessment, management and treatment. [ citation needed ]


Mothers who are negative for the Kell 1  antigen develop antibodies after being exposed to red blood cells that are positive for Kell 1 .  Over half of the cases of hemolytic disease of the newborn owing the anti-Kell antibodies are caused by multiple blood transfusions, with the remainder due to a previous pregnancy with a Kell 1  positive baby. [ citation needed ]


Hemolytic disease of the fetus and newborn (HDN) is a condition where the passage of maternal antibodies results in the hemolysis of fetal/neonatal red cells. The antibodies can be naturally occurring such as anti-A, and anti-B, or immune antibodies developed following a sensitizing event. [ 11 ]  Isoimmunization occurs when the maternal immune system is sensitized to red blood cell surface antigens. The most common causes of isoimmunization are blood transfusion, and fetal-maternal hemorrhage. [ 12 ]  The hemolytic process can result in anemia, hyperbilirubinemia, neonatal thrombocytopenia, and neonatal neutropenia. [ 6 ]  With the use of RhD Immunoprophylaxis, (commonly called Rhogam), the incidence of anti-D has decreased dramatically and other alloantibodies are now a major cause of HDN. [ 11 ]


Anti-Kell can cause severe anemia regardless of titer. [ 13 ]  Anti-Kell suppresses the bone marrow, [ 14 ]  by inhibiting the erythroid progenitor cells. [ 15 ] [ 16 ]


Hemolytic disease of the newborn can also be caused by anti-Kell 2 , anti-Kell 3  and anti-Kell 4  IgG antibodies.  These are rarer and generally the disease is milder. [ citation needed ]


Testing for HDN involves blood work from both mother and father, and may also include assessment with amniocentesis and Middle Cerebral Artery scans. [ citation needed ]


Blood testing for the mother is called an Indirect Coombs Test (ICT) or an Indirect Agglutination Test (IAT). This test tells whether there are antibodies in the maternal plasma. If positive, the antibody is identified and given a titer. Titers of 1:4 or higher is considered critical for Kell (compared to 1:16 for most other antibodies) and is considered to confer a high risk of fetal anemia. [ 17 ]  Such high titers may be managed by weekly follow-up by  obstetric ultrasound , assessing the peak systolic velocity of the fetal middle cerebral arterial (MCA), amniotic fluid volume, as well as fetal signs of anemia or hydrops. [ 17 ]


Blood is generally drawn from the father to help determine fetal antigen status. [ 18 ]  If he is homozygous for the antigen, there is a 100% chance of all offspring in the pairing to be positive for the antigen and at risk for HDN. If he is heterozygous, there is a 50% chance of offspring to be positive for the antigen. [ 19 ]  This test can help with knowledge for the current baby, as well as aid in the decision about future pregnancies. With RhD, the test is called the RhD genotype. With RhCE, and Kell antigen it is called an antigen phenotype. [ 20 ]


There are 3 possible ways to test the fetal antigen status. Cell-free DNA, Amniocentesis, and Chorionic Villus Sampling (CVS). Of the three, CVS is no longer used due to risk of worsening the maternal antibody response. Once antigen status has been determined, assessment may be done with MCA scans. [ citation needed ]


Middle cerebral artery - peak systolic velocity is changing the way sensitized pregnancies are managed. [ 22 ]  This test is done noninvasively with ultrasound. By measuring the peak velocity of blood flow in the middle cerebral artery, a MoM (multiple of the median) score can be calculated. MoM of 1.5 or greater indicates severe anemia and should be treated with  intrauterine transfusion  (IUT). [ 23 ] [ 22 ]


There are several intervention options available in early, mid and late pregnancies.


In some cases, the direct coombs will be negative but severe, even fatal HDN can occur. [ 35 ]  An indirect coombs needs to be run in cases of anti-C, [ 36 ]  anti-c, [ 36 ]  and anti-M. Anti-M also recommends antigen testing to rule out the presence of HDN. [ 26 ]


Suggestions have been made that women of child-bearing age or young girls should not be given a  transfusion  with Kell 1  positive blood. Donated blood is not currently screened (in the U.S.A.) for the Kell blood group antigens as it is not considered cost effective at this time. [ citation needed ]


It has been hypothesized [ by whom? ]  that IgG anti-Kell 1  antibody injections would prevent sensitization to RBC surface Kell 1  antigens in a similar way that IgG anti-D antibodies ( Rho(D) Immune Globulin ) are used to prevent  Rh disease , but the methods for IgG anti-Kell  1  antibodies have not been developed at the present time. [ citation needed ]


Once a woman has antibodies, she is at high risk for a transfusion reaction. [ 42 ]  For this reason, she must carry a medical alert card at all times and inform all doctors of her antibody status. [ citation needed ]


"Acute hemolytic transfusion reactions may be either immune-mediated or nonimmune-mediated. Immune-mediated hemolytic transfusion reactions caused by immunoglobulin M (IgM) anti-A, anti-B, or anti-A,B typically result in severe, potentially fatal complement-mediated intravascular hemolysis. Immune-mediated hemolytic reactions caused by IgG, Rh, Kell, Duffy, or other non-ABO antibodies typically result in extravascular sequestration, shortened survival of transfused red cells, and relatively mild clinical reactions. Acute hemolytic transfusion reactions due to immune hemolysis may occur in patients who have no antibodies detectable by routine laboratory procedures" [ 43 ]


Summary of transfusion reactions in the US [ 44 ]


Hemolytic disease of the newborn  ( anti-Rhc ) can range from a mild to a severe disease. It is the third most common cause of severe HDN.  Rh disease  is the most common and  hemolytic disease of the newborn (anti-Kell)  is the second most common cause of severe HDN. It occurs more commonly in women who are Rh D negative. [ citation needed ]


Once a woman has antibodies, she is at high risk for a transfusion reaction. [ 10 ]  For this reason, she must carry a medical alert card at all times and inform all doctors of her antibody status. [ citation needed ]


"Acute hemolytic transfusion reactions may be either immune-mediated or nonimmune-mediated. Immune-mediated hemolytic transfusion reactions caused by immunoglobulin M (IgM) anti-A, anti-B, or anti-A,B typically result in severe, potentially fatal complement-mediated intravascular hemolysis. Immune-mediated hemolytic reactions caused by IgG, Rh, Kell, Duffy, or other non-ABO antibodies typically result in extravascular sequestration, shortened survival of transfused red cells, and relatively mild clinical reactions. Acute hemolytic transfusion reactions due to immune hemolysis may occur in patients who have no antibodies detectable by routine laboratory procedures." [ 11 ]


A Rhc negative mother can become sensitised by  red blood cell  (RBC) Rhc antigens by her first pregnancy with a Rhc positive fetus.  The mother can make  IgG  anti-Rhc  antibodies , which are able to pass through the  placenta  and enter the fetal circulation.  If the fetus is Rhc positive  alloimmune   hemolysis  can occur leading to HDN.  This is similar as for  Rh disease , which is usually caused when a RhD negative mother is sensitised by her first pregnancy with a RhD positive fetus. [ citation needed ]


Sensitization to Rhc antigens can also be caused by blood transfusion. [ citation needed ]


Anti-C and anti-c can both show a negative DAT but still have a severely affected infant. [ 12 ] [ 13 ]  An indirect coombs must also be run.


In the case of anti-c, the woman should be checked around 28 weeks to see if she has developed anti-E as well. [ citation needed ]


Blood testing for the mother is called an Indirect Coombs Test (ICT) or an Indirect Agglutination Test (IAT). This test tells whether there are antibodies in the maternal plasma. If positive, the antibody is identified and given a titer. Critical titers are associated with significant risk of fetal anemia and hydrops. [ 14 ]  Titers of 1:8 or higher is considered critical for Kell. Titers of 1:16 or higher are considered critical for all other antibodies. After critical titer is reached, care is based on MCA scans. If antibodies are low and have a sudden jump later in pregnancy, an MCA scan is warranted. If the titer undergoes a 4 fold increase, it should be considered significant regardless of if the critical value has been reached. Maternal titers are not useful in predicting fetal anemia after the first affected gestation and should not be used for the basis of care. [ 15 ]  Titers are tested monthly until 24 weeks, after which they are done every 2 weeks. [ 16 ]


"In only 2 situations are patients not monitored identically to patients who are Rh sensitized. The first is that of alloimmunization to the c, E, or, C antigens. Some concern exists that hemolysis may occur in these patients with a lower than 1:16 titer. Thus, if the initial titer is 1:4 and stable but increases at 26 weeks' gestation to 1:8, assessment with MCA Doppler velocity at that point is reasonable. However, if the patient presents in the first trimester with a 1:8 titer that remains stable at 1:8 throughout the second trimester, continued serial antibody titers are appropriate.
The second situation in which patients should not be treated identically to patients who are Rh D sensitized is that of Kell isoimmunization because several cases of severe fetal hemolysis with anti-Kell antibodies have occurred in the setting of low titers." [ 14 ]


In the case of a positive ICT, the woman must carry a medical alert card or bracelet for life because of the risk of a transfusion reaction. [ 17 ]


There are 3 possible ways to test the fetal antigen status. Free Cell DNA, Amniocentesis, and Chorionic Villus Sampling (CVS). Of the three, CVS is no longer used due to risk of worsening the maternal antibody response. Once antigen status has been determined, assessment may be done with MCA scans. [ citation needed ]


MCA scans: Middle cerebral artery - peak systolic velocity is changing the way sensitized pregnancies are managed. [ 22 ]  This test is done noninvasively with ultrasound. By measuring the peak velocity of blood flow in the middle cerebral artery, a MoM (multiple of the median) score can be calculated. MoM of 1.5 or greater indicates severe anemia and should be treated with IUT. [ 23 ] [ 22 ]


It has been suggested that women of child-bearing age or young girls should not be given a  transfusion  with Rhc positive blood (or Kell  1  positive blood for similar reasons).  This would require a lot of extra work in blood transfusion departments and it is considered not economical to do the blood group screening at the present time. [ citation needed ]


It is theoretically likely that IgG anti-Rhc antibody injections would prevent sensitization to RBC surface Rhc antigens in a similar way that IgG anti-D antibodies ( Rho(D) immune globulin ) are used to prevent  Rh disease , but the methods for IgG anti-Rhc antibodies have not been developed at the present time. [ citation needed ]


In some cases, the direct coombs will be negative but severe, even fatal HDN can occur. [ 12 ]  An indirect coombs needs to be run in cases of anti-C, [ 13 ]  anti-c, [ 13 ]  and anti-M. Anti-M also recommends antigen testing to rule out the presence of HDN. [ 26 ]


Hemolytic disease of the fetus and newborn (HDN) is a condition where the passage of maternal antibodies results in the hemolysis of fetal/neonatal red cells. The antibodies can be naturally occurring such as anti-A, and anti-B, or immune antibodies developed following a sensitizing event. [ 38 ]  Isoimmunization occurs when the maternal immune system is sensitized to red blood cell surface antigens. The most common causes of isoimmunization are blood transfusion, and fetal-maternal hemorrhage. [ 16 ]  The hemolytic process can result in anemia, hyperbilirubinemia, neonatal thrombocytopenia, and neonatal neutropenia. [ 5 ]  With the use of RhD Immunoprophylaxis, (commonly called Rhogam), the incidence of anti-D has decreased dramatically and other alloantibodies are now a major cause of HDN. [ 38 ]


Hemolytic disease of the newborn  ( anti-RhE ) is caused by the anti-RhE antibody of the  Rh blood group system . The anti-RhE  antibody  can be naturally occurring, or arise following  immune  sensitization after a  blood transfusion  or pregnancy.


The anti-RhE antibody is quite common especially in the Rh genotype CDe/CDe; it usually only causes a mild hemolytic disease, but can cause a severe condition in the newborn.  It can occur with other antibodies, usually the anti-Rhc antibody, which can also cause a severe hemolytic disease. [ 1 ]


One study done by Moran et al., found that titers are not reliable for anti-E. Their most severe case of  hemolytic disease of the newborn  occurred with titers 1:2. Moran states that it would be unwise routinely to dismiss anti-E as being of little clinical consequence. [ 2 ]


Hemolytic disease of the fetus and newborn (HDN) is a condition where the passage of maternal antibodies results in the hemolysis of fetal/neonatal red cells. The antibodies can be naturally occurring such as anti-A, and anti-B, or immune antibodies developed following a sensitizing event. [ 12 ]  Isoimmunization occurs when the maternal immune system is sensitized to red blood cell surface antigens. The most common causes of isoimmunization are blood transfusion, and fetal-maternal hemorrhage. [ 13 ]  The hemolytic process can result in anemia, hyperbilirubinemia, neonatal thrombocytopenia, and neonatal neutropenia. [ 7 ]  With the use of RhD Immunoprophylaxis, (commonly called Rhogam), the incidence of anti-D has decreased dramatically and other alloantibodies are now a major cause of HDN. [ 12 ]


In the case of anti-E, the woman should be checked around 28 weeks to see if she has developed anti-c as well. [ citation needed ]


Blood testing for the mother is called an indirect  Coombs test  (ICT) or an indirect agglutination test (IAT). This test tells whether there are antibodies in the maternal plasma. If positive, the antibody is identified and given a titer. Critical titers are associated with significant risk of fetal anemia and hydrops. [ 1 ]  Titers of 1:8 or higher is considered critical for Kell. Titers of 1:16 or higher are considered critical for all other antibodies. After critical titer is reached, care is based on MCA scans. If antibodies are low and have a sudden jump later in pregnancy, an MCA scan is warranted. If the titer undergoes a 4 fold increase, it should be considered significant regardless of if the critical value has been reached. Maternal titers are not useful in predicting fetal anemia after the first affected gestation and should not be used for the basis of care. [ 14 ]  Titers are tested monthly until 24 weeks, after which they are done every 2 weeks. [ 13 ]


"In only 2 situations are patients not monitored identically to patients who are Rh sensitized. The first is that of alloimmunization to the c, E, or, C antigens. Some concern exists that hemolysis may occur in these patients with a lower than 1:16 titer. Thus, if the initial titer is 1:4 and stable but increases at 26 weeks' gestation to 1:8, assessment with MCA Doppler velocity at that point is reasonable. However, if the patient presents in the first trimester with a 1:8 titer that remains stable at 1:8 throughout the second trimester, continued serial antibody titers are appropriate.
The second situation in which patients should not be treated identically to patients who are Rh D sensitized is that of Kell isoimmunization because several cases of severe fetal hemolysis with anti-Kell antibodies have occurred in the setting of low titers." [ 1 ]


In the case of a positive ICT, the woman must carry a medical alert card or bracelet for life because of the risk of a transfusion reaction. [ citation needed ]


Blood is generally drawn from the father to help determine fetal antigen status. [ 15 ]  If he is homozygous for the antigen, there is a 100% chance of all offspring in the pairing to be positive for the antigen and at risk for HDN. If he is heterozygous, there is a 50% chance of offspring to be positive for the antigen. [ 16 ]  This test can help with knowledge for the current baby, as well as aid in the decision about future pregnancies. With RhD, the test is called the RhD genotype. With RhCE, and Kell antigen it is called an antigen phenotype. [ citation needed ]


There are three possible ways to test the fetal antigen status. Free cell DNA,  amniocentesis , and  chorionic villus sampling  (CVS). Of the three, CVS is no longer used due to risk of worsening the maternal antibody response. Once antigen status has been determined, assessment may be done with MCA scans. [ citation needed ]


Middle cerebral artery – peak systolic velocity is changing the way sensitized pregnancies are managed. [ 18 ]  This test is done noninvasively with ultrasound. By measuring the peak velocity of blood flow in the middle cerebral artery, a MoM (multiple of the median) score can be calculated. MoM of 1.5 or greater indicates severe anemia and should be treated with IUT. [ 19 ] [ 18 ]


There are several intervention options available in early, mid and late pregnancies. [ citation needed ]


In some cases, the direct Coombs will be negative but severe, even fatal HDN can occur. [ 29 ]  An indirect Coombs needs to be run in cases of anti-C, [ 30 ]  anti-c, [ 30 ]  and anti-M. Anti-M also recommends antigen testing to rule out the presence of HDN. [ 22 ]


Once a woman has antibodies, she is at high risk for a transfusion reaction. [ 36 ]  For this reason, she must carry a medical alert card at all times and inform all doctors of her antibody status. [ citation needed ]


"Acute hemolytic transfusion reactions may be either immune-mediated or nonimmune-mediated. Immune-mediated hemolytic transfusion reactions caused by immunoglobulin M (IgM) anti-A, anti-B, or anti-A,B typically result in severe, potentially fatal complement-mediated intravascular hemolysis. Immune-mediated hemolytic reactions caused by IgG, Rh, Kell, Duffy, or other non-ABO antibodies typically result in extravascular sequestration, shortened survival of transfused red cells, and relatively mild clinical reactions. Acute hemolytic transfusion reactions due to immune hemolysis may occur in patients who have no antibodies detectable by routine laboratory procedures." [ 37 ]


Summary of transfusion reactions in the US: [ 38 ]


Hemoperfusion  or  hæmoperfusion  (see  spelling differences ) is a method of filtering the  blood  extracorporeally (that is, outside the body) to remove a  toxin . As with other extracorporeal methods, such as  hemodialysis  (HD),  hemofiltration  (HF), and  hemodiafiltration  (HDF), the blood travels from the patient into a machine, gets filtered, and then travels back into the patient, typically by venovenous access (out of a  vein  and back into a vein).


In hemoperfusion, the blood perfuses a filter composed of  artificial cells  filled with  activated carbon  or another  microporous material . Small  molecules  in  solution  within the  serum  (such as the toxin) cross the membranes into the microporous material (and get trapped therein), but formed elements (the  blood cells ) brush past the artificial cells just as they brush past each other. In this way, the microporous material's filtering ability can be used  without destroying the blood cells .


First introduced in the 1940s, hemoperfusion was refined during the 1950s through 1970s, and then introduced clinically for the treatment of  poisoning  in the 1970s and 1980s. It is sometimes used to treat  drug overdose , sometimes in conjunction with the other extracorporeal techniques previously mentioned. [ 1 ]


The US  Food and Drug Administration  (FDA) defines sorbent hemoperfusion as follows:


″(a) Identification. A sorbent hemoperfusion system is a prescription device that consists of an extracorporeal blood system similar to that identified in the hemodialysis system and accessories (876.5820) and a container filled with adsorbent material that removes a wide range of substances, both toxic and normal, from blood flowing through it. The adsorbent materials are usually activated-carbon or resins which may be coated or immobilized to prevent fine particles entering the patient's blood. The generic type of device may include lines and filters specifically designed to connect the device to the extracorporeal blood system. The device is used in the treatment of poisoning, drug overdose, hepatic coma, or metabolic disturbances.″
 [ 2 ]


Hemoperfusion is also used in the treatment of specific intoxications, such as  valproic acid ,  theophylline , and  meprobamate . [ 3 ] [ 4 ]


Despite its availability, this technique is only infrequently utilized as a medical process used to remove toxic substances from a patient's blood. [ 5 ]


Two types of hemoperfusion are commonly used: [ citation needed ]


Complications of hemoperfusion may include  thrombocytopenia ,  leucopenia ,  hypoglycemia , and some reduction in clotting factors, with recovery typically occurring in 1–2 days. Risk of bleeding is also higher because of the high heparin dose and reduction in platelets and clotting factors. [ 6 ]


During hemoperfusion, the blood passes through a column with absorptive properties aiming at removing specific toxic substances from the patient's blood. It especially targets small- to medium-sized  molecules  that tend to be more difficult to remove by conventional  hemodialysis . The adsorbent substance most commonly used in hemoperfusion are resins and  activated carbon . [ 7 ]  Hemoperfusion is an  extracorporeal  form of treatment because the blood is pumped through a device outside the patient's body. [ citation needed ]


Its major uses include removing  drugs  or  poisons  from the blood in emergency situations, removing waste products from the blood in patients with  kidney failure , and as a supportive treatment for patients before and after  liver transplantation . [ 8 ]


Hemotherapy  ( / h iː m ə ˈ θ ɛr ə p i /   HEE -mə- THERR -ə-pee ) or  hemotherapeutics  ( / h iː m ə θ ɛr ə ˈ p juː t ɪ k s /   HEE -mə- THERR -ə- PEW -tiks ) is the treatment of  disease  by the use of  blood  or  blood products  from  blood donation  ( by others  or  for oneself ). [ 1 ]


It includes various types, such as: [ citation needed ]


hh , [ 1 ]  or the  Bombay blood  group, is a rare  blood type . This blood  phenotype  was first discovered in  Bombay  by Dr. Y. M. Bhende in 1952. It is mostly found in the  Indian subcontinent  ( India ,  Bangladesh ,  Pakistan ) and  Iran .


The first person found to have the Bombay phenotype had a blood type that reacted to other blood types in a way never seen before. The serum contained  antibodies  that attacked all  red blood cells  of normal  ABO phenotypes . The red blood cells appeared to lack all of the ABO blood group antigens and to have an additional antigen that was previously unknown. [ 1 ]


Individuals with the rare Bombay phenotype (hh) do not express  H antigen  (also called substance H), the antigen which is present in blood group O. As a result, they cannot make  A antigen  (also called substance A) or  B antigen  (substance B) on their red blood cells, whatever alleles they may have of the A and B blood-group genes, because A antigen and B antigen are made from H antigen.  For this reason people who have Bombay phenotype can donate red blood cells to any member of the ABO blood group system (unless some other blood factor gene, such as  Rh , is incompatible), but they cannot receive blood from any member of the ABO blood group system (which always contains one or more of A, B or H antigens), but only from other people who have Bombay phenotype. [ 1 ]


Receiving blood that contains an antigen which has never been in the patient's own blood causes an immune reaction due to the immune system of a hypothetical receiver producing immunoglobulins against that antigen—in the case of a Bombay patient, not only against antigens A and B, but also against H antigen.


In order to avoid complications during a  blood transfusion , it is very important to detect Bombay phenotype individuals, but the usual tests for ABO blood group system would show them as group O. Since anti-H  immunoglobulins  can activate the  complement cascade , it will lead to the lysis of red blood cells while they are still in the circulation, provoking an  acute hemolytic transfusion reaction . This cannot be prevented unless those typing the blood and providing care are aware of the existence of the Bombay blood group and have the means to test for it. [ citation needed ]


This very rare phenotype is generally present in about 0.0004% (about 4 per million) of the human population, though in some places such as  Mumbai  (formerly Bombay) locals can have occurrences in as much as 0.01% (1 in 10,000) of inhabitants. Given that this condition is very rare, any person with this blood group who needs an urgent blood transfusion will probably be unable to get it, as no  blood bank  would have any in stock. Those anticipating the need for blood transfusion may bank blood for their own use, but this option is not available in cases of accidental injury. For example, by 2017 only one  Colombian  person was known to have this phenotype, and blood had to be imported from  Brazil  for a transfusion. [ 2 ]  In 2023, it was reported that only three registered Brazilians nationwide possessed this phenotype. [ 3 ]


Biosynthesis  of the H, A and B antigens involves a series of  enzymes  (glycosyl transferases) that transfer  monosaccharides . The resulting antigens are  oligosaccharide  chains, which are attached to  lipids  and  proteins  that are anchored in the red blood cell membrane. The function of the H antigen, apart from being an intermediate substrate in the synthesis of ABO blood group antigens, is not known, although it may be involved in  cell adhesion . People who lack the H antigen do not suffer from deleterious effects, and being H-deficient is only an issue if they need a blood transfusion, because they would need blood without the H antigen present on red blood cells. [ citation needed ]


The specificity of the H antigen is determined by the sequence of  oligosaccharides . More specifically, the minimum requirement for H antigenicity is the terminal disaccharide  fucose - galactose , where the fucose has an alpha(1-2)linkage. This antigen is produced by a specific fucosyl transferase ( Galactoside 2-alpha-L-fucosyltransferase 2 ) that catalyzes the final step in the synthesis of the molecule. Depending upon a person's ABO blood type, the H antigen is converted into either the A antigen, B antigen, or both. If a person has group O blood, the H antigen remains unmodified. Therefore, the H antigen is present more in blood type O and less in blood type AB.


Two regions of the genome encode two enzymes with very similar substrate specificities: the H locus ( FUT1 ) which encodes the fucosyl transferase and the Se locus ( FUT2 ) that instead indirectly encodes a soluble form of the transferase, which is found in bodily secretions. Both genes are on  chromosome 19  at q.13.3. — FUT1 and FUT2 are tightly linked, being only 35 kb apart. Because they are highly  homologous , they are likely to have been the result of a gene duplication of a common gene ancestor.


The H locus contains four  exons  that span more than 8 kb of genomic DNA. Both the Bombay and para-Bombay phenotypes are the result of point mutations in the FUT1 gene. At least one functioning copy of FUT1 needs to be present (H/H or H/h) for the H antigen to be produced on red blood cells. If both copies of FUT1 are inactive (h/h), the Bombay phenotype results. The classical Bombay phenotype is caused by a Tyr316Ter mutation in the coding region of FUT1. The mutation introduces a stop codon, leading to a truncated enzyme that lacks 50 amino acids at the C-terminal end, rendering the enzyme inactive. In Caucasians, the Bombay phenotype may be caused by a number of mutations. Likewise, a number of mutations have been reported to underlie the para-Bombay phenotype. The Se locus contains the FUT2 gene, which is expressed in secretory glands. Individuals who are "secretors" (Se/Se or Se/se) contain at least one copy of a functioning enzyme. They produce a soluble form of H antigen that is found in saliva and other bodily fluids. "Non-secretors" (se/se) do not produce soluble H antigen. The enzyme encoded by FUT2 is also involved in the synthesis of antigens of the Lewis blood group.


Bombay phenotype occurs in individuals who have inherited two recessive alleles of the H gene (i.e. their genotype is hh). These individuals do not produce the H carbohydrate that is the precursor to the A and B antigens, meaning that individuals may possess alleles for either or both of the A and B alleles without being able to express them. Because both parents must carry this recessive allele to transmit this blood type to their children, the condition mainly occurs in small closed-off communities where there is a good chance of both parents of a child either being of Bombay type, or being heterozygous for the h allele and so carrying the Bombay characteristic as recessive. Other examples may include noble families, which are inbred due to custom rather than local genetic variety.


In theory, the maternal production of anti-H during pregnancy might cause hemolytic disease (HDN) in a fetus who did not inherit the mother's Bombay phenotype. In practice, cases of HDN caused in this way have not been described. This may be due to the rarity of the Bombay phenotype.


The term  human blood group systems  is defined by the  International Society of Blood Transfusion  (ISBT) as systems in the human species where cell-surface  antigens —in particular, those on blood cells—are "controlled at a single gene  locus  or by two or more very closely linked  homologous  genes with little or no observable  recombination  between them", [ 1 ]  and include the common  ABO  and  Rh (Rhesus)  antigen systems, as well as many others; 44 human systems are identified as of 31 December 2022 [update] . [ 2 ]


Following is a comparison of clinically relevant characteristics of antibodies against the main human blood group systems: [ 10 ]


Blood compatibility testing is performed before  blood transfusion , including matching of the  ABO blood group system  and the  Rh blood group system , as well as screening for recipient antibodies against other human blood group systems. Blood compatibility testing is also routinely performed on pregnant women and on the  cord blood  from newborn babies, because incompatibility puts the baby at risk for developing  hemolytic disease of the newborn . [ 13 ] [ 14 ]  It is also used before  hematopoietic stem cell transplantation , as it may be responsible for some cases of acute  graft-versus-host disease . [ 15 ]


Other human blood group systems than ABO and Rh have a relatively small risk of complications when blood is mixed. [ 16 ]  Therefore, in emergencies such as major  hemorrhage , the urgency of transfusion can exceed the need for compatibility testing against other blood group systems (and potentially Rh as well). [ 16 ]  Also, blood compatibility testing beyond ABO and Rh is generally limited to antibody detection (not necessarily including forward typing). Still, in Europe, females who require blood transfusions are often typed for the  K  and extended Rh antigens to prevent sensitization to these antigens, which could put them at risk for developing  hemolytic disease of the newborn  during pregnancy. [ 17 ]


When needing to give red blood cell transfusion to a patient, the presence of clinically significant antibodies produced by the patient can be detected by mixing patient serum with 2 to 4 "screening" or "control" red blood cells that together display essentially all relevant antigens. If any of these mixes display a reaction (evidence of patient antibodies binding to the screening red blood cells), a more extensive antibody panel is warranted (as imaged at right). [ 18 ]


The  human leukocyte antigen  ( HLA ) system is a complex of  genes  on  chromosome 6  in humans that encode  cell-surface proteins  responsible for regulation of the  immune system . [ 1 ]  The HLA system is also known as the human version of the  major histocompatibility complex  (MHC) found in many animals. [ 2 ]


Mutations in HLA genes may be linked to  autoimmune diseases  such as  type I diabetes , and  celiac disease . The HLA gene complex resides on a 3  Mbp  stretch within  chromosome 6, p-arm  at 21.3. HLA genes are highly  polymorphic , which means that they have many different  alleles , allowing them to fine-tune the  adaptive immune system . The proteins encoded by certain genes are also known as  antigens , as a result of their  historic discovery  as factors in  organ transplants . [ 3 ]


HLAs corresponding to  MHC class I  ( A ,  B , and  C ), all of which are the HLA Class1 group, present peptides from inside the cell. For example, if the cell is infected by a virus, the HLA system brings fragments of the virus to the surface of the cell so that the cell can be destroyed by the immune system. These peptides are produced from digested proteins that are broken down in the  proteasomes . In general, these particular peptides are small  polymers , of about 8-10  amino acids  in length. [ 4 ]  Foreign antigens presented by MHC class I attract T-lymphocytes called  killer T-cells  (also referred to as  CD8 -positive or cytotoxic T-cells) that destroy cells. Some new work has proposed that antigens longer than 10 amino acids, 11-14 amino acids, can be presented on MHC I, eliciting a cytotoxic T-cell response. [ 5 ]  MHC class I proteins associate with  β2-microglobulin , which, unlike the HLA proteins, is encoded by a gene on  chromosome 15 .


HLAs corresponding to  MHC class II  ( DP ,  DM ,  DO ,  DQ , and  DR ) present antigens from outside of the cell to T-lymphocytes. These particular antigens stimulate multiplication of  T-helper cells  (also called  CD4 -positive T cells), which in turn stimulate  antibody -producing  B-cells  to produce antibodies to that specific antigen. Self-antigens are suppressed by  regulatory T cells . Predicting which (fragments of) antigens will be presented to the immune system by a certain HLA type is difficult, but the technology involved is improving. [ 6 ]


HLAs corresponding to  MHC class III  encode components of the  complement system .


HLAs have other roles. They are important in disease defense. They are the major cause of  organ transplant rejection . They may protect against cancers or fail to protect (if down-regulated by an infection). [ 7 ]  HLA may also be related to people's perception of the odor of other people, and may be involved in mate selection, as at least one study found a lower-than-expected rate of HLA similarity between spouses in an isolated community. [ 8 ]


Aside from the genes encoding the six major antigen-presenting proteins, many other genes, many involved in immune function, are located on the HLA complex. Diversity of HLAs in the human population is one aspect of disease defense, and, as a result, the chance of two unrelated individuals with identical HLA molecules on all  loci  is extremely low. HLA genes have historically been identified as a result of the ability to successfully transplant organs between HLA-similar individuals. [ 9 ]


The  proteins  encoded by HLAs are those on the outer part of body cells that are (in effect) unique to that person. The  immune system  uses the HLAs to differentiate self cells and non-self cells. Any cell displaying that person's HLA type belongs to that person and is therefore not an invader.


When a foreign  pathogen  enters the body, specific  cells  called  antigen-presenting cells  (APCs) engulf the pathogen through a process called  phagocytosis .  Proteins  from the pathogen are digested into small pieces ( peptides ) and loaded on to HLA antigens (to be specific,  MHC class II ). They are then displayed by the  antigen-presenting cells  to  CD4+ helper T cells , [ 10 ]  which then produce a variety of effects and cell-to-cell interactions to eliminate the pathogen.


Through a similar process, proteins (both native and foreign, such as the proteins of viruses) produced inside most cells are displayed on HLAs (to be specific,  MHC class I ) on the cell surface. Infected cells can be recognized and destroyed by  CD8+ T cells . [ 10 ]


The image off to the side shows a piece of a poisonous bacterial protein (SEI peptide) bound within the binding cleft portion of the HLA-DR1 molecule. In the illustration far below, a different view, one can see an entire DQ with a bound peptide in a similar cleft, as viewed from the side. Disease-related peptides fit into these "slots" much like a hand fits into a glove.


When bound, peptides are presented to T-cells. T-cells require presentation via MHC molecules to recognize foreign antigens—a requirement known as  MHC restriction . T-cells have receptors that are similar to B-cell receptors, and each T-cell recognizes only a few MHC class II-peptide combinations. Once a T-cell recognizes a peptide within an MHC class II molecule, it can stimulate B-cells that also recognize the same molecule in their B-cell receptors. Thus, T-cells help B-cells make antibodies to the same foreign antigens. Each HLA can bind many peptides, and each person has 3 HLA types and can have 4 isoforms of DP, 4 isoforms of DQ and 4 Isoforms of DR (2 of DRB1, and 2 of DRB3, DRB4, or DRB5) for a total of 12 isoforms. In such heterozygotes, it is difficult for disease-related proteins to escape detection.


Any cell displaying some other HLA type is "non-self" and is seen as an invader by the body's immune system, resulting in the rejection of the tissue bearing those cells. This is particularly important in the case of transplanted tissue, because it could lead to  transplant rejection . Because of the importance of HLA in transplantation, the HLA loci are some of the most frequently typed by serology and PCR. It has been shown that high resolution HLA typing (HLA-A, HLA-B, HLA-C, HLA-DRB1, HLA-DQB1 and HLA-DPB1) may be relevant in transplantation to identify a full match, even when the donor is related. [ 11 ]


HLA types are inherited, and some of them are connected with  autoimmune disorders  and other diseases. People with certain HLA antigens are more likely to develop certain autoimmune diseases, such as  type I diabetes ,  ankylosing spondylitis ,  rheumatoid arthritis , [ 15 ]   celiac disease ,  SLE  (systemic lupus erythematosus),  myasthenia gravis ,  inclusion body myositis ,  Sjögren syndrome , and  narcolepsy . [ 16 ]


HLA typing has led to some improvement and acceleration in the diagnosis of celiac disease and type 1 diabetes; however, for DQ2 typing to be useful, it requires either high-resolution B1*typing (resolving *02:01 from *02:02), DQA1*typing, or DR  serotyping . Current serotyping can resolve, in one step, DQ8. HLA typing in autoimmunity is being increasingly used as a tool in diagnosis. In  celiac disease , it is the only effective means of discriminating between first-degree relatives that are at risk from those that are not at risk, prior to the appearance of sometimes-irreversible symptoms such as allergies and secondary autoimmune disease.


Some HLA-mediated diseases are directly involved in the promotion of cancer. Gluten-sensitive enteropathy is associated with increased prevalence of enteropathy-associated T-cell lymphoma, and DR3-DQ2 homozygotes are within the highest risk group, with close to 80% of gluten-sensitive enteropathy-associated T-cell lymphoma cases. More often, however, HLA molecules play a protective role, recognizing increases in antigens that are not tolerated because of low levels in the normal state. Abnormal cells might be targeted for  apoptosis , which is thought to mediate many cancers before diagnosis.


There is evidence for non-random  mate choice  with respect to certain genetic characteristics. [ 17 ] [ 18 ]  This has led to a field known as  genetic matchmaking .


MHC class I proteins form a functional receptor on most nucleated cells of the body. [ 1 ]


There are three major and three minor MHC class I genes in HLA.


Major MHC class I


Minor genes are  HLA-E ,  HLA-F  and  HLA-G .  β 2 -microglobulin  binds with major and minor gene subunits to produce a heterodimer.


There are three major and two minor MHC class II proteins encoded by the HLA.
The genes of the class II combine to form heterodimeric (αβ) protein
receptors that are typically expressed on the surface of  antigen-presenting cells .


Major MHC class II proteins only occur on  antigen-presenting cells ,  B cells , and  T cells . [ 1 ]


The other MHC class II proteins, DM and DO, are used in the internal processing of antigens, loading the antigenic peptides generated from pathogens onto the HLA molecules of  antigen-presenting cell .


Modern HLA alleles are typically noted with a variety of levels of detail. Most designations begin with HLA- and the locus name, then * and some (even) number of digits specifying the allele. The first two digits specify a group of alleles, also known as supertypes. Older typing methodologies often could not completely distinguish alleles and so stopped at this level. The third through fourth digits specify a nonsynonymous allele. Digits five through six denote any synonymous mutations within the coding frame of the gene. The seventh and eighth digits distinguish mutations outside the coding region. Letters such as L, N, Q, or S may follow an allele's designation to specify an expression level or other non-genomic data known about it. Thus, a completely described allele may be up to 9 digits long, not including the HLA-prefix and locus notation. [ 19 ]


MHC loci are some of the most genetically variable coding loci in mammals, and the human HLA loci are no exceptions. Despite the fact that the human population went through a constriction several times during its history that was capable of fixing many loci, the HLA loci appear to have survived such a constriction with a great deal of variation. [ 20 ]  Of the 9 loci mentioned above, most retained a dozen or more allele-groups for each locus, far more preserved variation than the vast majority of human loci. This is consistent with a heterozygous or  balancing selection  coefficient for these loci. In addition, some HLA loci are among the fastest-evolving coding regions in the human genome. One mechanism of diversification has been noted in the study of Amazonian tribes of South America that appear to have undergone intense  gene conversion  between variable alleles and loci within each HLA gene class. [ 21 ]  Less frequently, longer-range productive recombinations through HLA genes have been noted producing chimeric genes.


Six loci have over 100 alleles that have been detected in the human population. Of these, the most variable are HLA B and HLA DRB1. As of 2012, the number of alleles that have been determined are listed in the table below. To interpret this table, it is necessary to consider that an allele is a variant of the nucleotide (DNA) sequence at a locus, such that each allele differs from all other alleles in at least one (single nucleotide polymorphism, SNP) position. Most of these changes result in a change in the amino acid sequences that result in slight to major functional differences in the protein.


There are issues that limit this variation. Certain alleles like DQA1*05:01 and DQA1*05:05 encode proteins with identically processed products. Other alleles like DQB1*0201 and DQB1*0202 produce proteins that are functionally similar. For class II (DR, DP and DQ), amino acid variants within the receptor's peptide-binding cleft tend to produce molecules with different binding capability.


However, the gene frequencies of the most common alleles (>5%) of HLA-A, -B, -C and HLA-DPA1, -DPB1, -DQA1, -DQB1,  and -DRB1 from South America have been reported from the typing and sequencing carried out in genetic diversity studies and cases and controls. [ 22 ]  In addition, information on the allele frequencies of HLA-I and HLA-II genes for the European population has been compiled. [ 23 ] [ 24 ]  In both cases the distribution of allele frequencies reveals a regional variation related with the history of the populations.


Number of variant alleles at class I loci according to the IMGT-HLA database, last updated October 2018:


Number of variant alleles at class II loci (DM, DO, DP, DQ, and DR):


The large extent of variability in HLA genes poses significant challenges in investigating the role of HLA genetic variations in diseases. Disease association studies typically treat each HLA allele as a single complete unit, which does not illuminate the parts of the molecule associated with disease. Karp D. R. et al. describes a novel  sequence feature variant type  (SFVT) approach for HLA genetic analysis that categorizes HLA proteins into biologically relevant smaller sequence features (SFs), and their variant types (VTs). [ 27 ]  Sequence features are combinations of amino acid sites defined based on structural information (e.g., beta-sheet 1), functional information (e.g., peptide antigen-binding), and polymorphism. These sequence features can be overlapping and continuous or discontinuous in the linear sequence. Variant types for each sequence feature are defined based upon all known polymorphisms in the HLA locus being described. SFVT categorization of HLA is applied in genetic association analysis so that the effects and roles of the epitopes shared by several HLA alleles can be identified. Sequence features and their variant types have been described for all classical HLA proteins; the international repository of HLA SFVTs will be maintained at IMGT/HLA database. [ 28 ]   A tool to convert HLA alleles into their component SFVTs can be found on the Immunology Database and Analysis Portal (ImmPort) website. [ 29 ]


Although the number of individual HLA alleles that have been identified is large, approximately 40% of these alleles appear to be unique, having only been identified in single individuals. [ 30 ] [ 31 ]  Roughly a third of alleles have been reported more than three times in unrelated individuals. [ 31 ] [ 32 ]  Because of this variation in the rate at which of individual HLA alleles are detected, attempts have been made to categorize alleles at each expressed HLA locus in terms of their prevalence. The result is a catalog of common and well-documented (CWD) HLA alleles, [ 32 ] [ 33 ]  and a catalogue of rare and very rare HLA alleles. [ 30 ] [ 31 ]


Common HLA alleles are defined as having been observed with a frequency of at least 0.001 in reference populations of at least 1500 individuals. [ 32 ] [ 33 ]  Well-documented HLA alleles were originally defined as having been reported at least three times in unrelated individuals, [ 32 ]  and are now defined as having been detected at least five times in unrelated individuals via the application of a sequence-based typing (SBT) method, or at least three times via a SBT method and in a specific haplotype in unrelated individuals. [ 33 ]  Rare alleles are defined as those that have been reported one to four times, and very rare alleles as those reported only once. [ 30 ] [ 31 ]


While the current CWD and rare or very rare designations were developed using different datasets and different versions of the  IMGT/HLA Database , [ 31 ] [ 33 ]  the approximate fraction of alleles at each HLA locus in each category is shown below.


There are two parallel systems of nomenclature that are applied to HLA. The first, and oldest, system is based on serological (antibody based) recognition. In this system, antigens were eventually assigned letters and numbers (e.g.,  HLA-B27  or, shortened, B27). A parallel system that allowed more refined definition of alleles was developed. In this system, an "HLA" is used in conjunction with a letter, *, and a four-or-more-digit number (e.g., HLA-B*08:01, A*68:01, A*24:02:01N N=Null) to designate a specific  allele  at a given HLA  locus . HLA loci can be further classified into  MHC class I  and  MHC class II  (or rarely, D locus). Every two years, a nomenclature is put forth to aid researchers in interpreting serotypes to alleles. [ 25 ]


In order to create a typing reagent, blood from animals or humans would be taken, the blood cells allowed to separate from the serum, and the serum diluted to its optimal sensitivity and used to type cells from other individuals or animals. Thus, serotyping became a way of crudely identifying HLA receptors and receptor isoforms. Over the years, serotyping antibodies became more refined as techniques for increasing sensitivity improved and new serotyping antibodies continue to appear. One of the goals of serotype analysis is to fill gaps in the analysis. It is possible to predict based on 'square root','maximum-likelihood' method, or analysis of familial haplotypes to account for adequately typed alleles. These studies using serotyping techniques frequently revealed, in particular for non-European or north East Asian populations many null or blank serotypes. This was particularly problematic for the Cw locus until recently, and almost half of the Cw serotypes went untyped in the 1991 survey of the human population.


There are several types of serotypes. A broad antigen serotype is a crude measure of identity of cells. For example, HLA A9 serotype recognizes cells of A23- and A24-bearing individuals. It may also recognize cells that A23 and A24 miss because of small variations. A23 and A24 are split antigens, but antibodies specific to either are typically used more often than antibodies to broad antigens.


A representative cellular assay is the mixed lymphocyte culture (MLC) and used to determine the HLA class II types. [ 34 ]  The cellular assay is more sensitive in detecting HLA differences than serotyping. This is because minor differences unrecognized by alloantisera can stimulate T cells. This typing is designated as Dw types. Serotyped DR1 has cellularly defined as either of Dw1 or of Dw20 and so on for other serotyped DRs. Table [ 35 ]  shows associated cellular specificities for DR alleles. However, cellular typing has inconsistency in the reaction between cellular-type individuals, sometimes resulting differently from predicted. Together with difficulty of cellular assay in generating and maintaining cellular typing reagents, cellular assay is being replaced by DNA-based typing method. [ 34 ]


Minor reactions to subregions that show similarity to other types can be observed to the gene products of alleles of a serotype group. The sequence of the antigens determines the antibody reactivities, and so having a good sequencing capability (or sequence-based typing) obviates the need for serological reactions. Therefore, different serotype reactions may indicate the need to sequence a person's HLA to determine a new gene sequence.


Broad antigen types are still useful, such as typing very diverse populations with many unidentified HLA alleles (Africa, Arabia, [ 36 ]  Southeastern Iran [ 37 ]  and Pakistan, India [ 38 ] ). Africa, Southern Iran, and Arabia show the difficulty in typing areas that were settled earlier. Allelic diversity makes it necessary to use broad antigen typing followed by gene sequencing because there is an increased risk of misidentifying by serotyping techniques.


In the end, a workshop, based on sequence, decides which new allele goes into which serogroup either by sequence or by reactivity. Once the sequence is verified, it is assigned a number. For example, a new allele of B44 may get a serotype (i.e. B44) and allele ID i.e. B*44:65, as it is the 65th B44 allele discovered. Marsh et al. (2005) [ 25 ]  can be considered a code book for HLA serotypes and genotypes, and a new book biannually with monthly updates in  Tissue Antigens .


Gene typing is different from gene sequencing and serotyping.
With this strategy, PCR primers specific to a variant region of DNA are used (called sequence-specific primers). If a product of the right size is found, the assumption is that the HLA allele has been identified. New gene sequences often result in an increasing appearance of ambiguity. Because gene typing is based on SSP-PCR, it is possible that new variants, in particular in the class I and DRB1 loci, may be missed.


For example, SSP-PCR within the clinical situation is often used for identifying HLA phenotypes. An example of an extended phenotype for a person might be:


A *01:01 / *03:01 , C *07:01 / *07:02 , B *07:02 / *08:01 , DRB1 *03:01 / *15:01 , DQA1 *05:01 / *01:02 , DQB1 *02:01 / *06:02


In general, this is identical to the extended serotype:
A1,A3,B7,B8,DR3,DR15(2), DQ2,DQ6(1)


For many populations, such as the Japanese or European populations, so many patients have been typed that new alleles are relatively rare, and thus SSP-PCR is more than adequate for allele resolution. Haplotypes can be obtained by typing family members in areas of the world where SSP-PCR is unable to recognize alleles and typing requires the sequencing of new alleles. Areas of the world where SSP-PCR or serotyping may be inadequate include Central Africa, Eastern Africa, parts of southern Africa, Arabia, S. Iran, Pakistan, and India.


An HLA haplotype is a series of HLA "genes" (loci-alleles) by chromosome, one passed from the mother and one from the father.


The phenotype exampled above is one of the more common in Ireland and is the result of two common genetic  haplotypes :


A *01:01  ; C *07:01  ; B *08:01  ; DRB1 *03:01  ; DQA1 *05:01  ; DQB1 *02:01
(By serotyping  A1-Cw7-B8-DR3-DQ2 )


which is called ' 'super B8' ' or ' 'ancestral haplotype' ' and


A *03:01  ; C *07:02  ; B *07:02  ; DRB1 *15:01  ; DQA1 *01:02  ; DQB1 *06:02
(By serotyping A3-Cw7-B7-DR15-DQ6 or the older version  "A3-B7-DR2-DQ1")


These haplotypes can be used to trace migrations in the human population because they are often much like a fingerprint of an event that has occurred in evolution. The Super-B8 haplotype is enriched in the Western Irish, declines along gradients away from that region, and is found only in areas of the world where Western Europeans have migrated. The "A3-B7-DR2-DQ1" is more widely spread, from Eastern Asia to Iberia. The Super-B8 haplotype is associated with a number of diet-associated autoimmune diseases. There are 100,000s of extended haplotypes, but only a few show a visible and nodal character in the human population.


Studies of humans and animals imply a heterozygous selection mechanism operating on these loci as an explanation for this variability. [ 39 ]  One proposed mechanism is sexual selection in which females are able to detect males with different HLA relative to their own type. [ 40 ]   While the DQ and DP encoding loci have fewer alleles, combinations of A1:B1 can produce a theoretical potential of 7,755 DQ and 5,270 DP αβ heterodimers, respectively. While nowhere near this number of isoforms exist in the human population, each individual can carry 4 variable DQ and DP isoforms, increasing the potential number of antigens that these receptors can present to the immune system.


Studies of the variable positions of DP, DR, and DQ reveal that peptide antigen contact residues on class II molecules are most frequently the site of variation in the protein primary structure. Therefore, through a combination of intense allelic variation and/or subunit pairing, the class II peptide receptors are capable of binding an almost endless variation of peptides of 9 amino acids or longer in length, protecting interbreeding subpopulations from nascent or epidemic diseases. Individuals in a population frequently have different haplotypes, and this results in many combinations, even in small groups. This diversity enhances the survival of such groups, and thwarts evolution of epitopes in pathogens, which would otherwise be able to be shielded from the immune system.


HLA antibodies are typically not naturally occurring, and with few exceptions are formed as a result of an immunologic challenge to a foreign material containing non-self HLAs via blood transfusion, pregnancy (paternally inherited antigens), or organ or tissue transplant.


Antibodies against disease-associated HLA haplotypes have been proposed as a treatment for severe autoimmune diseases. [ 41 ]


Donor-specific HLA antibodies have been found to be associated with graft failure in renal, heart, lung, and liver transplantation. These donor-specific HLA antibodies can exist pretransplant as consequence of sensitization to prior transplants or through pregnancies, but also occur de novo post-transplantation. There is a clear link between the risk of HLA antibody sensitisation and the donor-recipient HLA (molecular) mismatch. [ 42 ]


In some diseases requiring  hematopoietic stem cell transplantation ,  preimplantation genetic diagnosis  may be used to give rise to a sibling with matching HLA, although there are ethical considerations. [ 43 ]


Human platelet antigens (HPA)  are  polymorphisms  in  platelet   antigens . These can stimulate production of  alloantibodies  (that is,  antibodies  against other people's antigens) in recipients of  transfused  platelets from  donors  with different HPAs. These antibodies cause  neonatal alloimmune thrombocytopenia ,  post-transfusion purpura , and some cases of  platelet transfusion refractoriness  to infusion of donor platelets. [ 1 ]


A  nomenclature  was devised by International Society of Blood Transfusion (ISBT), platelet working party to overcome problems generated by many different nomenclatures in use. Since inception of this list, a greater number of antigens have been described and the molecular basis of many has been resolved. [ citation needed ]


To date, 24 platelet-specific alloantigens have been defined by  immune sera , of which 12 are grouped in six biallelic systems (HPA-1, -2, -3, -4, -5, -15). For the remaining 12,  alloantibodies  against the  thetical  but not the  antithetical  antigen have been observed. The molecular basis of 22 of the 24 serologically defined antigens has been resolved. In all but one of the 22, the difference between self and non-self is defined by a single amino acid substitution generally caused by a  single-nucleotide polymorphism  (SNP). [ citation needed ]


Iatrogenic anemia , also known as  nosocomial anemia  or  hospital-acquired anemia , is a condition in which a person develops  anemia  due to medical interventions, most frequently repeated  blood draws . [ 1 ] [ 2 ] [ 4 ]  Other factors that contribute to iatrogenic anemia include bleeding from medical procedures and dilution of the blood by  intravenous fluids . [ 2 ]  People may receive  blood transfusions  to treat iatrogenic anemia, which carries risks for complications like  transfusion reactions  and  circulatory overload . [ 3 ] [ 5 ]


A 2013 study of over 400,000 people admitted to US hospitals found that 74% developed anemia at some point during their hospital stay. [ 5 ]  Iatrogenic anemia is of particular concern in  intensive care medicine , [ 6 ] : 629   because people who are critically ill require frequent blood tests and have a higher risk of developing anemia due to lower  hemoglobin  levels and impaired production of red blood cells ( erythropoesis ) at baseline. The average  intensive care unit  (ICU) patient loses up to 660 mL of blood per week to laboratory testing. [ 3 ]  For each day in the ICU, it is estimated that a person's hemoglobin level falls by 5 g/L (0.5 g/dL), 80% of which is due to phlebotomy. [ 7 ] : 20   On the second day of admission to the ICU, more than 70% of adults exhibit anemia, over half of whom will go on to require a  blood transfusion . [ 3 ]


In the  neonatal intensive care unit  (NICU), the issue is exacerbated by the patients' low body weight: it is estimated that during their first six weeks of life, infants in NICUs may lose 15−30% of their blood volume to blood draws. [ 3 ] [ 8 ]  Premature babies often suffer from  anemia of prematurity , which is caused by low production of  erythropoietin  (a hormone that stimulates red blood cell production) and the short lifespan of neonates' red blood cells, and is worsened by blood loss through phlebotomy. [ 9 ]


People who are receiving  dialysis  lose blood not only through sampling for laboratory tests, but from the dialysis process itself and from bleeding caused by accessing veins to attach the dialysis equipment. This iatrogenic anemia often occurs alongside the anemia caused by  kidney disease . [ 6 ] : 629


Another factor that contributes to anemia in hospitalized people is the use of  intravenous fluids . Infusion with large volumes of intravenous fluids dilutes the blood, causing a decreased hemoglobin and hematocrit level. This is not a true anemia, as no red blood cells are lost and the body eventually compensates for the effects of the infusion. However, the decreased hemoglobin and hematocrit may lead to unnecessary transfusion. Blood loss through surgery and through medical procedures such as  central line  placement also play a role, as does the use of certain drugs which can suppress the  bone marrow 's ability to produce red blood cells. [ 2 ]


People who develop iatrogenic anemia spend a longer amount of time in the hospital and have an increased risk of mortality. They are also more likely to receive  blood transfusions , [ 1 ]  which carries risks for various conditions, including  transfusion reactions ,  lung injury ,  circulatory overload  and  alloimmunization . [ 2 ] [ 3 ]  After the initial development of anemia, further testing may be ordered to monitor and investigate the condition, which worsens the anemia and the attendant risks for complications. [ 1 ]


The volume of blood needed for most laboratory tests is  lower than the amount that is commonly drawn; a 2008 study found that only 9% of the blood in standard sized blood tubes was used for testing. Using smaller tubes for blood tests can decrease the risk of anemia, but it may increase the risk of laboratory errors. [ 3 ]   Point-of-care testing , meaning testing performed at a patient's bedside rather than in a  medical laboratory , typically uses much smaller blood volumes than conventional testing;  [ 7 ] : 20   however, as of 2019, there is insufficient evidence regarding the effects of point-of-care testing on iatrogenic anemia. The use of closed blood sampling devices, which return excess blood from blood draws or  line flushes  to the person's circulation, can decrease the amount of blood loss in hospitalized patients. [ 3 ]  Strategies to decrease the amount of blood tests ordered, such as clinician education and  auditing , or restricting test orders through the  electronic health record , have also been investigated. [ 1 ]


The  LW blood system  was first described by  Landsteiner  and  Wiener  in 1940. [ 1 ]  It was often confused with the  Rh  system, not becoming a separate antigen system until 1982. The LW and RhD antigens are genetically independent though they are phenotypically related and the LW antigen is expressed more strongly on RhD positive cells than on RhD negative cells. In most populations, the antithetical LW antigens, LW a  and LW b  are present as very high and very low frequency, respectively. [ 1 ] [ 2 ] [ 3 ]


The LW locus is located on the short arm of  chromosome 19  (19p13.3). [ 1 ]


LW antigens reside on a 40- to 42-kilo dalton  red cell membrane  glycoprotein  named  CD242 . [ 2 ]  The LW glycoprotein has recently been renamed ICAM-4 due to its similarity to  intercellular adhesion molecule , although exactly which  integrins  bind to ICAM-4 is subject to controversy.


The function of ICAM-4 is not fully understood but appears to be restricted to  erythroid  cells. During in vitro  erythropoesis , LW appears at either the erythroid colony forming stage or later at the proerythroblast stage. A vital part of erythropoesis is the clustering of erythroblasts around  bone marrow   macrophages  to form erythroblastic islands. The erythroblast is then able to remove its  nucleus , which is in turn ingested and broken down by the macrophages, to become a mature  erythrocyte . During this process ICAM-4 binds to VLA-4, an erythroblast binding site, on adjacent erythroblasts and to  αv integrins  on macrophages to help stabilise the erythroblastic islands. The binding of red cells to macrophages in the spleen by ICAM-4 could also play a part in the removal of senescent red cells. [ 1 ] [ 2 ] [ 3 ]


Despite the functional aspects of ICAM-4, its apparent absence in LW(a-b-) and Rh null  phenotypes does not appear to lead to any obvious pathological effects. ICAM-4 expression is elevated on sickle red cells and its binding to αv integrins on the endothelial cells may cause the pain associated with  sickle cell  crises. [ 1 ] [ 2 ]


Auto anti-LW is not uncommon as an  autoantibody  but usually presents with transient suppression of the LW antigen in genetically LW+ individuals, and so appears to be an  alloantibody . True alloanti-LW is a very rare occurrence, with only two known examples of alloanti-LW ab , produced by patients with an LW(a-b-) phenotype. Anti-LW can be present as a clinically insignificant autoantibody and not be associated with increased red cell destruction. Anti-LW has also been associated with cases of warm type  autoimmune haemolytic anaemia ;  Philip Levine  suggested that it was the most common antibody in cases of AIHA with a positive  Coombs test . [ 1 ] [ 4 ] [ 5 ]


Haemolytic disease of the newborn  (HDFN) due to alloanti-LW is described as mild and very rare, even the very potent anti-LW ab  of one known patient caused minimal evidence of HDFN in her three pregnancies. [ 6 ]  To date auto anti-LW has only been implicated as the cause of one case of HDFN. [ 7 ]


The  Ii antigen system  is a  human blood group system  based upon  a gene  on  chromosome 6  and consisting of the  I antigen  and the  i antigen . [ 1 ]  The I antigen is normally present on the cell membrane of  red blood cells  in all adults, while the i antigen is present in  fetuses  and newborns. [ 2 ]


Adult red blood cells express I antigen abundantly. [ 3 ]  Developing fetuses and newborns express i antigen until around 13-20 months after birth, when I antigen starts to be expressed instead. [ 3 ]  Like  ABH antigens , which make up the ABO blood group, I and i antigens are not restricted to the red blood cell membrane, but are found on most human cells and in body fluids such as  saliva . [ 1 ]


The I and i antigens are  carbohydrate  structures composed of repeating units of  N -acetyllactosamine  (LacNAc), and are located on the interior of structures carrying ABH and  Lewis  antigens. [ 1 ] [ 3 ]  LacNAc repeats are made by the enzymes  B3GNT1  and  B4GALT1 . [ 4 ]  The i antigen is made of linear repeats, while the structure of the I antigen is branched. [ 3 ]  Unlike most other blood groups, the two antigens are not encoded by different  alleles ; rather,  I-branching enzyme  converts i antigen to I antigen by adding branches. [ 5 ] [ 6 ]  The gene encoding I-branching enzyme is located on chromosome 6. [ 6 ]


The function of I and i antigens are unknown but may be related to  hematopoiesis , the production of blood. [ 6 ]  The rapid conversion from i to I antigens after birth suggests that I antigen plays an important role in adult red blood cells. [ 3 ]  The presence of the linear i antigen in fetuses, rather than the branched I antigen, may have developed as an  evolutionary  mechanism to prevent  ABO hemolytic disease of the fetus and newborn . [ 1 ]  Enhanced expression of i antigen is associated with conditions involving  stress hematopoiesis  such as  leukemia  and  sickle cell disease . [ 7 ]


Transient  autoantibodies  against I antigen are common, especially after infection by  Mycoplasma pneumoniae , and are rarely significant except in  cold agglutinin disease . [ 1 ]  Transient antibodies against i antigen are common after  infectious mononucleosis  and are also not clinically significant. [ 1 ]  Antibodies which recognize both I and i antigens are termed anti-j antibodies. [ 1 ]


The autoantibodies involved in cold agglutinin disease are usually against I antigen. [ 8 ]  The antibodies are usually  IgM  ( kappa  subtype), unlike transient autoantibodies which are generally  IgG . [ 1 ]  Cold-reactive IgM antibodies ( cold agglutinins ) bind to I antigen on red blood cells, and unlike IgG, are able to cause  agglutination  of red blood cells and activate  complement  to cause  hemolysis , leading to  anemia . [ 1 ] [ 8 ]


Rarely, individuals have the i antigen on their red blood cells into adulthood, known as the adult i phenotype. [ 1 ]  This is due to the presence of a  mutation  in the  GCNT2 gene  which encodes the I-branching enzyme. [ 1 ] [ 3 ]  These individuals have  alloantibodies  against the I antigen, though these are typically cold agglutinins and are unlikely to cause  transfusion reactions . [ 2 ] [ 9 ]


The adult i phenotype is associated with  congenital cataracts , most markedly in Japanese and Taiwanese people and least markedly in Caucasian people. [ 1 ] [ 6 ]  Cataracts occur when i antigen rather than I antigen is present on the  epithelium  of the  lens , due to a mutation in the form of the I-branching enzyme which is expressed in lens epithelium, IGNTB. [ 10 ]


The adult i phenotype is inherited in a  recessive  manner. [ 1 ]


The I antigen was first described in 1956 and the i antigen was discovered in 1960. [ 1 ]  I and i were the first discovered antigens which change significantly during  human development . [ 4 ]  The letter I was chosen to reflect the "individuality" of a person studied who lacked the I antigen. [ 6 ]


A similar blood group system with a developmental change resembling the Ii system (with human neonatal cells expressing i antigen and adult cells expressing I antigen) has been observed in most  primates , including  chimpanzees  and  monkeys . [ 1 ]  This is not seen in non-primates:  cats ,  dogs , or  guinea pigs . [ 1 ]


Immunoglobulin therapy  is the use of a mixture of  antibodies  (normal human immunoglobulin) to treat several health conditions. [ 13 ] [ 14 ]  These conditions include  primary immunodeficiency ,  immune thrombocytopenic purpura ,  chronic inflammatory demyelinating polyneuropathy ,  Kawasaki disease , certain cases of  HIV/AIDS  and  measles ,  Guillain–Barré syndrome , and certain other infections when a more specific immunoglobulin is not available. [ 13 ]  Depending on the formulation it can be given by  injection into muscle , a  vein , or  under the skin . [ 13 ]  The effects last a few weeks. [ 14 ]


Common side effects include pain at the site of injection, muscle pain, and  allergic reactions . [ 13 ]  Other severe side effects include  kidney problems ,  anaphylaxis ,  blood clots , and  red blood cell breakdown . [ 13 ]  Use is not recommended in people with some types of  IgA deficiency . [ 13 ]  Use appears to be relatively safe during  pregnancy . [ 13 ]  Human immunoglobulin is made from human  blood plasma . [ 13 ]  It contains antibodies against many  viruses . [ 14 ]


Human immunoglobulin therapy first occurred in the 1930s and a formulation for injection into a vein was approved for medical use in the United States in 1981. [ 15 ]  It is on the  World Health Organization's List of Essential Medicines . [ 16 ] [ 17 ]  Each formulation of the product is somewhat different. [ 14 ]  A number of  specific immunoglobulin  formulations are also available including for  hepatitis B ,  rabies ,  tetanus ,  varicella infection , and  Rh positive blood exposure . [ 14 ]


Immunoglobulin therapy is used in a variety of conditions, many of which involve decreased or abolished antibody production capabilities, which range from a complete absence of multiple types of antibodies, to  IgG subclass deficiencies  (usually involving IgG2 or IgG3), to other disorders in which antibodies are within a normal quantitative range, but lacking in quality – unable to respond to antigens as they normally should – resulting in an increased rate or increased severity of infections. In these situations, immunoglobulin infusions confer passive resistance to infection on their recipients by increasing the quantity/quality of  IgG  they possess. Immunoglobulin therapy is also used for a number of other conditions, including in many autoimmune disorders such as  dermatomyositis  in an attempt to decrease the severity of symptoms. Immunoglobulin therapy is also used in some treatment protocols for  secondary immunodeficiencies   such as  human immunodeficiency virus  (HIV), some autoimmune disorders (such as  immune thrombocytopenia  and  Kawasaki disease ), some neurological diseases ( multifocal motor neuropathy ,  stiff person syndrome ,  multiple sclerosis  and  myasthenia gravis ) some acute infections and some complications of organ transplantation. [ 18 ]


Immunoglobulin therapy is especially useful in some acute infection cases such as  pediatric   HIV  infection and is also considered the standard of treatment for some autoimmune disorders such as  Guillain–Barré syndrome . [ 19 ] [ 20 ]  The high demand which coupled with the difficulty of producing immunoglobulin in large quantities has resulted in increasing global shortages, usage limitations and rationing of immunoglobulin. [ 21 ]


The Australian Red Cross Blood Service developed their own guidelines for the appropriate use of immunoglobulin therapy in 1997. [ 22 ]  Immunoglobulin is funded under the National Blood Supply and indications are classified as either an established or emerging therapeutic role or conditions for which immunoglobulin use is in exceptional circumstances only. [ 23 ]


Subcutaneous immunoglobulin access programs have been developed to facilitate hospital based programs. [ 24 ]


Human normal immunoglobulin (human immunoglobulin G) (Cutaquig) was approved for medical use in Australia in May 2021. [ 25 ]


The National Advisory Committee on Blood and Blood Products of Canada (NAC) and Canadian Blood Services have also developed their own separate set of guidelines for the appropriate use of immunoglobulin therapy, which strongly support the use of immunoglobulin therapy in primary immunodeficiencies and some complications of HIV, while remaining silent on the issues of sepsis, multiple sclerosis, and chronic fatigue syndrome. [ 26 ]


Brands include HyQvia (human normal immunoglobulin), Privigen (human normal immunoglobulin (IVIg)), Hizentra (human normal immunoglobulin (SCIg)), Kiovig (human normal immunoglobulin), and Flebogamma DIF (human normal immunoglobulin). [ 12 ] [ 27 ] [ 28 ] [ 29 ]


In the EU human normal immunoglobulin (SCIg) (Hizentra) is used in people whose blood does not contain enough antibodies (proteins that help the body to fight infections and other diseases), also known as immunoglobulins. [ 27 ]  It is used to treat the following conditions:


It is indicated for replacement therapy in adults and children in primary immunodeficiency syndromes such as:


Flebogamma DIF is indicated for the replacement therapy in adults, children and adolescents (0–18 years) in:


and for the immunomodulation in adults, children and adolescents (0–18 years) in:


The United Kingdom's  National Health Service  recommends the routine use of immunoglobulin for a variety of conditions including primary immunodeficiencies and a number of other conditions, but recommends against the use of immunoglobulin in  sepsis  (unless a specific toxin has been identified), multiple sclerosis, neonatal sepsis, and pediatric  HIV/AIDS . [ 31 ]