There are two general approaches for RBC cryopreservation, referred to as the high- and the low-glycerol method. Glycerol serves as cryoprotectant in both. The high-glycerol method uses 40% weight/volume glycerol, a slow freezing rate (1–3 °C per minute) and allows storage of the frozen red blood cells in common mechanical −60–80 °C freezers. The low-glycerol method is based on 20% weight/volume glycerol and demands plunge freezing in (−150 °C) liquid nitrogen. Because of the extreme storage temperature, the low-glycerol method is not compatible with the PVC tubes of blood bags. PVC tubes are essential for sterile docking; a technology which maintains a closed system after thawing and, thereby, allows a longer post-thawing shelf-life. Because of this, and also because the high-glycerol method seems to protect the red blood cells better and is associated with less haemolysis than the low-glycerol method, the high-glycerol method is often preferred. [ 49 ] [ 50 ]


Pathogen reduction is a technology predominantly used to reduce the risk of transfusion-transmitted infectious diseases and bacterial contamination. The principle resembles the one of irradiation: by adding an agent which interferes with the replication process of DNA or RNA, any present pathogen, as well as any residual leucocytes, will not be able to replicate further. [ 51 ] [ 52 ]


Systems for pathogen inactivation of red blood cells are still awaiting market authorisation. However, studies suggest that the red blood cell quality is not negatively impacted by this processing procedure, which indicates that pathogen inactivation may be a suitable future substitute for irradiation and potentially also washing of red blood cells. [ 53 ] [ 54 ]


Red blood cell rejuvenation is a method which aims to increase the levels of  2,3-diphosphoglycerate  (2,3-DPG) and  ATP  in stored red blood cell concentrates, as the levels of both 2,3-DPG and ATP decrease over time. The rejuvenation process includes incubation of the red blood cells with a rejuvenation solution and subsequent washing. [ 55 ]  ATP is an important driver of a number of metabolic functions of the red blood cell, and declined ATP levels have been linked to reduced post-transfusion  in vivo  survival of the red blood cells. High levels of 2,3-DPG facilitates oxygen unloading from the red blood cells in the capillaries. [ 56 ]


Red blood cell concentrates can be modified to be suitable for paediatric patients. These modifications include split of regular units into smaller units (usually 3 – 6 parts), which facilitates limiting the number of involved donors at repeated transfusions. The modification can also be red blood cells for intrauterine transfusion where, in short, the additive solution is removed, which increases the haematocrit to between 0.70 – 0.85. [ 38 ]  A red blood cell concentrate can also be tailored for exchange transfusions for neonates. During this process, the additive solution is removed and instead, plasma is added to resemble a “whole blood”. Both at intrauterine and exchange transfusion, compatibility [ 1 ]  between the foetus/baby and the mother is of great importance.


Adverse events related to transfusion in general may include  allergic reactions  such as  anaphylaxis ,  infection ,  volume overload , and  lung injury .  With current screening methods, the risk of  viral infections  such as  hepatitis C  and  HIV/AIDS  are less than one in a million. [ 1 ]   With current testing methods in high-income countries the  prevalence of transfusion-transmissible infections in blood donations is very low (median: HIV 0.002%, hepatitis B 0.02%, hepatitis C 0.007% and syphilis 0.02% in 2024). However, in low-income countries the risk of a blood donation being positive for  HIV ,  hepatitis C  or  syphilis  is up to 1%, and the risk of it being  hepatitis B  positive was approximately 2.8% in 2024.  The differences relate to variations in eligible blood donors, whether the donation is paid or voluntary, non-remunerated, and the effectiveness of the system of educating and selecting donors. [ 57 ]


Adverse events related to transfusion of red blood cells are mainly linked to incompatibility issues or other transfusion reactions. Incompatible AB0 transfusion can be fatal. [ 58 ]  For patients with a previous transfusion reaction history, the risk of repeated adverse events can be mitigated by choosing the proper processing modification and/or red blood cell phenotype combination.


In the United Kingdom they cost about £120 per unit. [ 59 ]


The product is typically abbreviated  RBC ,  pRBC ,  PRBC , sometimes  StRBC , or even  LRBC  (the latter being to indicate those that have been leukoreduced, which is now true for the vast majority of RBC units). The name "Red Blood Cells" with initial capitals indicates a standardized blood product in the  United States . [ 60 ]  Without capitalization, it is simply generic without specifying whether or not the cells comprise a blood product, patient blood, etc. (with other generic terms for it being "erythrocyte" and "red cell"). [ citation needed ]


Plasminogen activators  are  serine proteases  that catalyze the activation of  plasmin  via proteolytic cleavage of its  zymogen  form  plasminogen . Plasmin is an important factor in  fibrinolysis , the breakdown of  fibrin  polymers formed during blood clotting. There are two main plasminogen activators:  urokinase (uPA)  and  tissue plasminogen activator (tPA).  Tissue plasminogen activators are used to treat medical conditions related to blood clotting including embolic or thrombotic stroke, myocardial infarction, and pulmonary embolism. [ 1 ]


Plasminogen activators are inhibited by  plasminogen activator inhibitor-1 ,  plasminogen activator inhibitor-2 , and  protein C inhibitor .


Produced mainly in the liver, plasminogen is the inactive zymogen form of plasmin, and circulates in plasma in a closed conformation that cannot be activated.  Binding clots or cell surfaces cause their conformation to change, allowing them to be activated by plasminogen activators. Plasminogen activators do so by cleaving the R561/V562 peptide bond, producing the active protein plasmin, which catalyzes the degradation of fibrin polymers that make up the structure of blood clots. [ 2 ]


The main inhibitor of tissue plasminogen activator and urokinase is plasminogen activator inhibitor-1 (PAI-1). [ 3 ]  Plasminogen activator inhibitor-1 is a serine protease, synthesized by endothelial cells, that specifically inhibits  tissue plasminogen activator  (tPA) and  urokinase  (uPA). Tissue plasminogen activator and urokinase are the activators of  plasminogen  and result in the breakdown of blood clots ( fibrinolysis ). [ 4 ]


PAI-1 levels have also been studied in patients and how they influence certain diseases. Elevated serum levels of PAI-1 have been found in obese individuals. [ 5 ]   Elevated levels of PAI-1 also seem to increase the risk of atherothrombotic events and may also promote vascular disease. [ 6 ]


Plasminogen activator inhibitor-2 (PAI-2) is a serine protease that inactivates tPA and uPA. PAI-2 is produced by the placenta and only found in high quantities in the blood during pregnancy. [ 7 ]


Factor XIa and XIIa are two main factors involved in the plasminogen activator. Factor XI (FXI) is a serine protase produced by the liver and circulates in its inactive form. [ 8 ]  Deficiency in factor XI is known to cause  hemophilia C . [ 9 ]   Factor XIIa is another plasma protein that is involved in the activation of zymogen factor is activated into factor XIa. [ 10 ]  This activation is important to the coagulation cascade.


Due to its contribution to fibrinolysis, tissue plasminogen activator is used medically to treat blood clot-related disorders including  thrombotic  or  embolic stroke ,  myocardial infarction , and  pulmonary embolism . It is manufactured using recombinant techniques and is sold as alteplase, reteplase, and tenecteplase.  Alteplase was the first of these versions to go on the market, and has the same structure as tPA.  Reteplase and tenecteplase both received FDA approval after alteplase, and have nonidentical structures to tPA. [ 1 ]  These recombinant forms of tPA have been shown to have a longer half-life in the blood and greater resistance to inhibition, resulting in  an increased capacity to treat thrombolytic diseases. [ 11 ]


Urokinase is similarly used in the medical field, specifically for the treatment of pulmonary embolism. [ 12 ]


1B2I ,  1BML ,  1BUI ,  1CEA ,  1CEB ,  1DDJ ,  1HPJ ,  1HPK ,  1I5K ,  1KI0 ,  1KRN ,  1L4D ,  1L4Z ,  1PK4 ,  1PKR ,  1PMK ,  1QRZ ,  1RJX ,  2DOH ,  2DOI ,  2KNF ,  2L0S ,  2PK4 ,  3UIR ,  4A5T ,  4CIK ,  4DCB ,  4DUR ,  4DUU ,  5HPG


NM_001168338 NM_000301


NP_000292 NP_001161810


Plasminogen activator inhibitor-1 not only functions as an inhibitor, but other roles of PAI-1 could suggest it could contribute to cancer. The other roles of PAI-1 include, cell de-adhesion, cell proliferation, apoptosis, and cell signaling. These roles could suggest that PAI-1 expression in the tumor microenvironment enhances tumor cell progression. Urokinase cleaves the zymogen plasminogen into serine protease plasmin. The elevated levels of uPA are an indicator of cancer which could be found in the carcinoma of the breast. Plasmin can activate matrix metalloproteases (MMP's) in the extracellular matrix (ECM). MMP activation contributes to tumor cell invasion and metastasis by degradation of ECM components. [ 5 ]


Platelet adhesiveness  is the adhesion of  platelets  to other structures. [ 1 ]


It can be contrasted with  platelet aggregation , [ citation needed ]  which refers to the processes or factors which lead to the adhesion of platelets to other platelets.


The  platelet plug,  also known as the  hemostatic plug  or  platelet thrombus , is an aggregation of  platelets  formed during early stages of  hemostasis  in response to one or more injuries to  blood vessel   walls . After platelets are recruited and begin to accumulate around the breakage, their “sticky” nature allows them to adhere to each other. This forms a platelet plug, which prevents more blood from leaving the body as well as any outside contaminants from getting in. The plug provides a temporary blockage of the break in the vasculature. As such, platelet plug formation occurs after  vasoconstriction  of the blood vessels but before the creation of the fibrin mesh clot, which is the more permanent solution to the injury. The result of the platelet plug formation is the coagulation of blood. It can also be referred to as primary hemostasis.


For many years, the critical role that platelets (also known as thrombocytes) played in hemostasis and blood coagulation went unnoticed by scientists. Even though the existence of platelets as a cell fragment was initially discovered in 1882, it took scientists until the 1960s before they moved their interest from the interaction of platelets with blood coagulation to the interaction of platelets with themselves. [ 1 ]


The discovery of  adenosine diphosphate  (ADP) as the primary inducer of platelet aggregation was a major breakthrough in the field of hematology. [ 2 ]  It was followed by the discovery of the platelet release reaction, as well as the aggregating properties of  thrombin  and  collagen .


The platelet plug formation is the second step of hemostasis. It occurs after vasoconstriction. During the process, platelets begin to accumulate, or aggregate, on the damaged vessel wall. [ citation needed ]


Platelet plug formation occurs in three major steps:


Under normal physiological conditions, blood flows through the body without any noticeable aggregation of platelets. This is because platelets are not initially programmed to accumulate by themselves because this could cause an undesirable thrombosis. However, during hemostasis, coagulation is desired. As such, the platelets in the plasma must be alerted to the need for a plug formation. [ citation needed ]


Any discontinuity detected in the vascular endothelium triggers an automatic response in the clotting system, which in turns stimulates thrombin production. [ 3 ]  Thrombin also causes platelet aggregation.


As such, more often than not, platelet adhesion and activation occur in overlapping steps, where one directly influences and contributes to the other.


Once platelets are activated, when they come across injured endothelium cells, the  von Willebrand factor (vWF)  and  fibrinogen  will act as anchors to allow platelets to adhere onto the vessel wall. [ 4 ]  These molecules are released from the platelet themselves as a result of degranulation, a physiological change in the platelet's shape due to the secretion of the contents of the dense granules and alpha granules. [ 4 ]  From the dense granules, serotonin and adenosine diphosphate are released. From the alpha granules come molecules such as the platelet-derived growth factor, fibrinogen, and the von Willebrand factor (vWF), a glycoprotein critical in platelet activation and adhesion. [ 4 ]


The ADP secreted from the dense granules then binds to receptors on the membrane of platelets. However, to allow for platelet adhesion to occur requires an additional molecule. Glycoprotein lb is a protein on the surface of the platelet membrane that binds to vWF. [ 3 ]  When vWF is bound to glycoprotein lb, it helps the platelet interact with other surfaces, like the inside of a damaged vessel wall. At high shear stress levels, the GP1b-von Willebrand Factor will initiate the platelet adhesion. [ 5 ]  This process will then be mediated by integrins, such as β1 (α2β1, α5β1) and β3 (αIIbβ3) integrins.


In addition, platelets are activated, they will also change shape in their cortical actin cytoskeleton. [ 6 ]  The platelets will transform from smooth, biconcave discs to fully spread cells. This dramatically increases their surface area and therefore allows for both increased blockage of the damaged cells as well as more space for adhesion to occur.


After platelets make contact with the focal point of the vascular injury, they begin to interact with each other to form a platelet aggregate. Platelet aggregation is mainly mediated by β3 (αIIbβ3) integrin and its ligands, such as vWF and fibrinogen. [ 4 ]   While platelet membranes have binding sites for fibrinogen, they must be induced by thrombin. Thrombin triggers the binding of the adhesive platelets with vWF and fibrinogen. [ 4 ]  ADP can then catalyze the aggregation of platelets, allowing for fibrinogen to link two platelets together. [ citation needed ]


As more platelets accumulate, they release more chemicals, which in turn attract even more platelets. This is a positive feedback loop that eventually results in the formation of the platelet thrombus.


A secondary hemostatic plug is formed after the temporary blockage is created. This process involves the conversion of fibrinogen, a soluble glycoprotein, into  fibrin , an insoluble glycoprotein, using the enzyme  thrombin . The fibrinogen forms fibrin to encase the platelet thrombus, thus creating a secondary hemostatic plug that is much more stable and securely attached to the vessel wall. [ 4 ]


Due to the shear force, a platelet thrombus attached to the blood vessel's walls can easily be swept away or disintegrated. As such, after the platelets have been anchored to the vessel wall, have been linked together, and have been enmeshed in fibrin, they must also be consolidated to ensure they can withstand such force. This is accomplished by  factor XIII , also known as fibrin stabilizing factor, an enzyme that crosslinks fibrin. Factor XIII is critical in the consolidation of a hemostatic plug. Those who are found to be deficient in the enzyme exhibit delayed bleeding after surgical procedures. [ 4 ]


While platelet activation and plug formation are necessary for the cessation of bleeding and vascular injuries, if platelet adhesion and aggregation occur in an unwarranted location, the result will instead be vascular obstruction and thrombosis. This is commonly observed in myocardial infarctions, in which platelet aggregation and adhesion result in a blocked coronary artery. [ 4 ]  As such, the same factors that cause platelets to coagulate during hemostasis can also contribute to unwanted thrombosis.


While the general mechanisms of hemostasis and platelet plug formation have already been discovered, there is still much to learn in terms of the chemicals contributing to the process. Only the key factors have been identified; there are still many molecules present during hemostasis that scientists do not understand the role they play. [ citation needed ]


Fibrinogen and vWF are known critical factors in hemostasis. However, it has been discovered that even in mice who lack both of these components, hemostasis and thrombosis still occur. [ 4 ]  This seems to suggest that there are other contributing molecules still undiscovered that may also play an important role in platelet aggregation and adhesion.


Platelet-activating factor , also known as  PAF ,  PAF-acether  or  AGEPC  (acetyl-glyceryl-ether-phosphorylcholine), is a potent  phospholipid  activator and mediator of many  leukocyte  functions,  platelet  aggregation and degranulation,  inflammation , and  anaphylaxis . It is also involved in changes to vascular permeability, the oxidative burst, chemotaxis of leukocytes, as well as augmentation of  arachidonic acid  metabolism in phagocytes.


PAF is produced by a variety of cells, but especially those involved in host defense, such as  platelets ,  endothelial  cells,  neutrophils ,  monocytes , and  macrophages . PAF is continuously produced by these cells but in low quantities and production is controlled by the activity of  PAF acetylhydrolases . It is produced in larger quantities by inflammatory cells in response to specific stimuli. [ 1 ]


PAF was discovered by French immunologist  Jacques Benveniste  in the early 1970s. [ 2 ] [ 3 ]  PAF was the first  phospholipid  known to have messenger functions. Benveniste made significant contributions in the role and characteristics of PAF and its importance in inflammatory response and mediation. Using lab rats and mice, he found that ionophore  A23187  (a mobile ion carrier that allows the passage of Mn 2+ , Ca 2+  and Mg 2+  and has antibiotic properties against bacteria and fungi)  caused the release of PAF. These developments led to the finding that macrophages produce PAF and that macrophages play an important function in aggregation of platelets and liberation of their inflammatory and vasoactive substances. [ citation needed ]


Further studies on PAF were conducted by Constantinos A. Demopoulos in 1979. [ 4 ]  Demopoulos found that PAF plays a crucial role in heart disease and strokes. His experiment’s data found that  atherosclerosis  (the accumulation of lipid-rich lesions in the  endothelium  of the arteries) can be attributed to PAF and PAF-like lipids, and identified biologically active compounds in the  polar   lipid  fractions of  olive oil , honey,  milk  and  yoghurt ,  mackerel , and  wine  that have PAF-antagonistic properties and inhibit the development of atherosclerosis in animal models. [ 5 ]  During the course of his studies, he also determined the chemical structure of the compound.


PAF can be found in  protozoans ,  yeasts ,  plants ,  bacteria , and  mammals . PAF has regulatory role in protozoans. The regulatory role is thought to diverge from that point and be maintained as living organisms started to evolve. During evolution, functions of PAF in the cell have been changing and enlarging. [ citation needed ]


PAF has been found in plants but its function has not yet been determined. [ citation needed ]


PAF is used to transmit signals between neighboring cells and acts as a  hormone ,  cytokines , and other signaling molecules. The PAF signaling system can trigger inflammatory and  thrombotic  cascades, amplify these cascades when acting with other mediators, and mediate molecular and cellular interactions ( cross talk ) between inflammation and thrombosis. [ 6 ]   Unregulated PAF signaling can cause pathological inflammation and has been found to be a cause in  sepsis ,  shock , and traumatic injury. PAF can be used as a local signaling molecule and travel over very short distances or it can be circulated throughout the body and act via  endocrine .


PAF initiates an inflammatory response in allergic reactions. [ 7 ]   This has been demonstrated in the skin of humans and in the paws and skin of lab rabbits and rodents. The inflammatory response is enhanced by the use of vasodilators, including prostaglandin E1 (PGE,) and PGE2 and inhibited by vasoconstrictors. [ 8 ]


PAF also induces apoptosis in a different way that is independent of the  PAF receptor . The pathway to apoptosis can be inhibited by negative feedback from PAF acetylhydrolase (PAF-AH), an enzyme that catabolizes platelet-activating factor.


It is an important mediator of  bronchoconstriction .


It causes platelets to aggregate and blood vessels to dilate. Thus, it is important to the process of  hemostasis . At a concentration of 10 −12  mol/L, PAF causes life-threatening inflammation of the airways to induce  asthma  like symptoms.


Toxins  such as fragments of destroyed bacteria induce the synthesis of PAF, which causes a drop in  blood pressure  and reduced volume of blood pumped by the heart, which leads to  shock  and possibly death.


Several molecular species of platelet-activating factor that vary in the length of the O-alkyl side-chain have been identified.


Studies found that PAF could not be modified without losing its  biological activity . Thus, small changes in the structure of PAF could render its signaling abilities inert. [ 9 ]  Investigation led to the understanding that platelet and blood pressure response were dependent on the sn-2 propionyl analog. If the sn-1 was removed then PAF lacked any sort of biological activity. Finally, the sn-3 position of PAF was experimented with by removing methyl groups sequentially. As more and more methyl groups were removed, biological activity diminished until it was eventually inactive.


PAF is produced by stimulated basophils, monocytes, polymorphonuclear neutrophils, platelets, and endothelial cells primarily through lipid remodeling. A variety of stimuli can initiate the synthesis of PAF. These stimuli could be macrophages going through phagocytosis or endothelium cells uptake of thrombin.


There are two different pathways in which PAF can be synthesized:  de novo  pathway and remodeling. The remodeling pathway is activated by inflammatory agents and it is thought to be the primary source of PAF under pathological conditions. The  de novo  pathway is used to maintain PAF levels during normal cellular function.


The most common pathway taken to produce PAF is remodeling. The precursor to the remodeling pathway is a phospholipid, which is typically phosphatidylcholine (PC).  The fatty acid is removed from the sn-2 position of the three-carbon backbone of the phospholipid by phospholipase A2 (PLA2) to produce the intermediate lyso-PC (LPC). An acetyl group is then added by LPC acetyltransferase (LPCAT) to produce PAF.


Using the  de novo  pathway, PAF is produced from  1-O-alkyl-2-acetyl-sn-glycerol  (AAG). Fatty acids are joined on the sn-1 position with 1-O-hexadecyl being the best for PAF activity.  Phosphocholine  is then added to the sn-3 site on AAG creating PAF.


The concentration of PAF is controlled by the synthesis of the compound and by the actions of PAF acetylhydrolases (PAF-AH).  PAF-AH are a family of enzymes that have the ability to catabolize and degrade PAF and turn it into an inactive compound.  The enzymes within this family are  lipoprotein-associated phospholipase A2 , cytoplasmic  platelet-activating factor acetylhydrolase 2 , and  platelet-activating factor acetylhydrolase 1b .


Cations are one form of regulation in the production of PAF. Calcium plays a large role in the inhibition of enzymes that produce PAF in the  denovo  pathway of PAF biosynthesis.


The regulation of PAF is still not completely understood. Enzymes that are associated with the production of PAF are controlled by metal  ions ,  thiol  compounds,  fatty acids ,  pH , compartmentalization, and phosphorylation and dephosphorylation. These controls on these PAF producing enzymes are believed to work in conjunction to control it, but the overall pathway and reasoning is not well understood.


PAF antagonists do not provoke an inflammatory response upon binding, but block or lessen the effect of PAF. Examples of PAF antagonists are: [ 10 ]


High PAF levels are associated with a variety of medical conditions. Some of these conditions include:


•Allergic reactions
•Stroke
•Sepsis
•Myocardial infarction
•Colitis, inflammation of the large intestine
•Multiple sclerosis


While the effects that PAF has on inflammatory response and cardiovascular conditions are well understood, PAF is still a subject for discussion. Over the past 23 years, papers written on PAF have almost doubled from approximately 7,500 in 1997 to 14,500 in 2020. PubMed (June 2020).  "Platelet-activating factor search results and historical activity metrics" . PubMed.  Research into PAF is ongoing.


The  Pratt Test  is a simple test to check for  deep vein thrombosis  in the  leg . [ 1 ] [ 2 ]   It involves having the patient lie supine with the leg bent at the  knee , grasping the calf with both  hands  and pressing on the  popliteal vein  in the proximal calf.  If the patient feels  pain , it is a sign that a deep vein thrombosis exists. [ citation needed ]


This  medical sign  article is a  stub . You can help Wikipedia by  expanding it .


1AUT ,  1LQV ,  3F6U ,  3JTC ,  4DT7


NM_001042767 NM_001042768 NM_008934 NM_001313938


NP_001362535 NP_001362536 NP_001362537 NP_001362538 NP_001362539 NP_001362540 NP_001362542


NP_001036232 NP_001036233 NP_001300867 NP_032960


Protein C , also known as  autoprothrombin IIA  and  blood coagulation factor XIV , [ 5 ] : 6822  [ 6 ]  is a  zymogen , that is, an inactive enzyme. The activated form plays an important role in regulating  anticoagulation ,  inflammation , and  cell death  and maintaining the  permeability  of blood vessel walls in humans and other animals.  Activated protein C  ( APC ) performs these operations primarily by  proteolytically  inactivating proteins  Factor V a  and  Factor VIII a . APC is classified as a  serine protease  since it contains a  residue  of  serine  in its  active site . [ 7 ] : 35   In humans, protein C is encoded by the  PROC   gene , which is found on  chromosome 2 . [ 8 ]


The zymogenic form of protein C is a  vitamin K -dependent  glycoprotein  that circulates in  blood plasma . Its structure is that of a two-chain polypeptide consisting of a light chain and a heavy chain connected by a  disulfide bond . [ 8 ] : 4673   The protein C zymogen is activated when it binds to  thrombin , another protein heavily involved in coagulation, and protein C's activation is greatly promoted by the presence of  thrombomodulin  and  endothelial protein C receptors  (EPCRs). Because of EPCR's role, activated protein C is found primarily near endothelial cells (i.e., those that make up the walls of blood vessels), and it is these cells and  leukocytes  (white blood cells) that APC affects. [ 7 ] : 34  [ 9 ] : 3162   Because of the crucial role that protein C plays as an  anticoagulant , those with deficiencies in protein C, or some kind of  resistance to APC , suffer from a significantly increased risk of forming dangerous blood clots ( thrombosis ).


Research into the clinical use of a  recombinant  form of human Activated Protein C (rhAPC) known as  Drotrecogin alfa-activated , branded Xigris by  Eli Lilly and Company , has been surrounded by controversy. Eli Lilly ran an aggressive marketing campaign to promote its use for people with severe  sepsis  and septic shock and sponsored the 2004  Surviving Sepsis Campaign  Guidelines. [ 10 ]  However, a 2012  Cochrane review  found that its use cannot be recommended since it does not improve survival and increases bleeding risk. [ 11 ]  In October 2011, Xigris was withdrawn from the market by Eli Lilly due to a higher mortality in a trial among adults. [ 12 ]


Protein C's  anticoagulant  role in the human body was first noted by Seegers  et al.  in 1960, [ 13 ]  who gave protein C its original name,  autoprothrombin II-a . [ 5 ] : 6822   Protein C was first isolated by  Johan Stenflo  from  bovine   plasma  in 1976, and Stenflo determined it to be a  vitamin K-dependent protein . [ 14 ]  He named it protein  C  because it was the third protein ("peak C") that  eluted  from a  DEAE-Sepharose   ion-exchange chromotograph . Seegers was, at the time, searching for vitamin K-dependent coagulation factors undetected by  clotting assays , which measure global clotting function. Soon after this, Seegers recognised Stenflo's discovery was identical with his own. [ 5 ] : 6822   Activated protein C was discovered later that year, [ 15 ]  and in 1977 it was first recognised that APC inactivates Factor V a . [ 16 ] : 2382  [ 17 ]  In 1980, Vehar and Davie discovered that APC also inactivates Factor VIII a , [ 18 ]  and soon after,  Protein S  was recognised as a  cofactor  by Walker. [ 19 ]  In 1982, a family study by Griffin  et al . first associated  protein C deficiency  with symptoms of  venous thrombosis . [ 20 ]  Homozygous protein C deficiency and the consequent serious health effects were described in 1984 by several scientists. [ 21 ] : 1214   cDNA cloning of protein C was first performed in 1984 by Beckmann  et al.  which produced a map of the gene responsible for producing protein C in the liver. [ 22 ]  In 1987 a seminal experiment was performed (Taylor  et al. ) whereby it was demonstrated that activated protein C prevented  coagulopathy  and death in baboons  infused  with lethal concentrations of  E. coli . [ 16 ] : 2382  [ 23 ]


In 1993, a heritable resistance to APC was detected by  Dahlbäck   et al.  and associated with familial  thrombophilia . [ 24 ]   In 1994, the relatively common genetic mutation that produces  Factor V Leiden  was noted (Bertina  et al. ). [ 25 ]  Two years later, Gla-domainless APC was imaged at a resolution of 2.8  Ångströms . [α] [ 5 ]   Beginning with the PROWESS  clinical trial  of 2001, [ 26 ]  it was recognised that many of the symptoms of  sepsis  may be ameliorated by infusion of APC, and mortality rates of septic patients may be significantly decreased. [ 9 ] : 3161, 6   Near the end of that year,  Drotrecogin alfa (activated) , a recombinant human activated protein C, became the first drug approved by the U.S.  FDA   for treating severe  sepsis . [ 27 ]  In 2002,  Science  published an article that first showed protein C activates  protease-activated receptor-1  (PAR-1) and this process accounts for the protein's modulation of the immune system. [ 16 ] : 2382  [ 28 ]


The biologic instructions for synthesising protein C in humans are encoded in the gene officially named "protein C (inactivator of coagulation factors Va and VIIIa)". The gene's symbol approved by the  HUGO Gene Nomenclature Committee  is "PROC" from " pro tein  C ". It is located on the second  chromosome  (2q13-q14) and comprises nine  exons . [ 8 ] [ 16 ] : 2383   The nucleotide sequence that codes for human protein C is approximately 11,000 bases long. [ 8 ] : 4675


Human protein C is a vitamin K-dependent glycoprotein structurally similar to other vitamin K-dependent proteins affecting blood clotting, [ 29 ]  such as  prothrombin ,  Factor VII ,  Factor IX  and  Factor X . [ 21 ] : 1215   Protein C synthesis occurs in the liver and begins with a single-chain precursor molecule: a 32 amino acid  N-terminus   signal peptide  preceding a  propeptide . [ 30 ] : S11   Protein C is formed when a  dipeptide  of Lys 198  and Arg 199  is removed; this causes the transformation into a  heterodimer  with  N -linked carbohydrates on each chain. The protein has one light chain (21  kDa ) and one heavy chain (41 kDa) connected by a  disulfide bond  between Cys 183  and Cys 319 .


Inactive protein C comprises 419 amino acids in multiple  domains : [ 16 ] : 2383   one  Gla domain  (residues 43–88); a helical  aromatic  segment (89–96); two  epidermal growth factor (EGF)-like domains  (97–132 and 136–176); an activation peptide (200–211); and a  trypsin -like serine protease domain (212–450). The light chain contains the Gla- and EGF-like domains and the aromatic segment. The heavy chain contains the protease domain and the activation petide. It is in this form that 85–90% of protein C circulates in the plasma as a  zymogen , waiting to be activated. [ 5 ] : 6822   The remaining protein C zymogen comprises slightly modified forms of the protein. Activation of the enzyme occurs when a thrombin molecule cleaves away the activation peptide from the  N-terminus  of the heavy chain. [ 8 ] : 4673
 [ 30 ] : S11   The active site contains a  catalytic triad  typical of serine proteases (His 253 , Asp 299  and Ser 402 ). [ 16 ] : 2833


The Gla domain is particularly useful for binding to negatively charged  phospholipids  for anticoagulation and to EPCR for  cytoprotection . One particular  exosite  augments protein C's ability to inactivate Factor V a  efficiently. Another is necessary for interacting with thrombomodulin. [ 16 ] : 2833


Post-translational modifications . Human Protein C has at least five types of  post-translational modifications : (1) gamma- carboxylation  on the first nine  glutamic acid  residues in the protein sequence. This modification event is performed by a vitamin K-dependent microsomal carboxylase. The full complement of Gla is required to give full activity to protein C. (2) beta- Hydroxylation  of Asp71 in one of the two  EGF-like domains  to give erythro-L-beta-hydroxy-aspartate (bHA). The modification is required for functional activity as was demonstrated by mutating Asp71 to Glu. (3) N-linked  glycosylation  at three possible glycosylation sites. Plasma human Protein C has been reported to be 23% carbohydrate by weight. (4) Disulfide formation. (5) Multiple  proteolytic cleavages  of the polypeptide backbone to remove an 18 amino acid  signal peptide , a 24 amino acid propeptide and then cleavages at amino acids 155-156 and 157-158 to yield the two-chain structure of the circulating zymogen. [ 31 ]


The activation of protein C is strongly promoted by  thrombomodulin  and  endothelial protein C receptor  (EPCR), the latter of which is found primarily on  endothelial cells  (cells on the inside of blood vessels). The presence of thrombomodulin accelerates activation by several orders of magnitude, [ 7 ] : 34   and EPCR speeds up activation by a factor of 20. If either of these two proteins is absent in  murine  specimens, the mouse dies from excessive blood-clotting while still in an  embryonic  state. [ 32 ] : 1983  [ 33 ] : 43335   On the endothelium, APC performs a major role in regulating blood clotting, inflammation, and cell death ( apoptosis ). [ 34 ] : 28S   Because of the accelerating effect of thrombomodulin on the activation of protein C, the protein may be said to be activated not by thrombin but the thrombin–thrombomodulin (or even thrombin–thrombomodulin–EPCR) complex. [ 16 ] : 2381   Once in active form, APC may or may not remain bound to EPCR, to which it has approximately the same affinity as the protein zymogen. [ 9 ] : 3162


Protein C in  zymogen  form is present in normal adult human  blood plasma  at concentrations between 65 and 135  IU / dL . Activated protein C is found at levels approximately 2000 times lower than this. [ 9 ] : 3161    Mild protein C deficiency corresponds to plasma levels above 20 IU/dL, but below the normal range. Moderately severe deficiencies describe blood concentrations between 1 and 20 IU/dL; severe deficiencies yield levels of protein C that are below 1 IU/dL or are undetectable. Protein C levels in a healthy  term infant  average 40 IU/dL. The concentration of protein C increases until six months, when the mean level is 60 IU/dL; the level stays low through childhood until it reaches adult levels after  adolescence . [ 21 ] : 1216   The  half-life  of activated protein C is around 15 minutes. [ 5 ] : 6823


The protein C pathways are the specific chemical reactions that control the level of expression of APC and its activity in the body. [ 7 ] : 34   Protein C is  pleiotropic , with two main classes of functions: anticoagulation and cytoprotection (its direct effect on cells). Which function protein C performs depends on whether or not APC remains bound to EPCR after it is activated; the anticoagulative effects of APC occur when it does not. In this case, protein C functions as an anticoagulant by irreversibly proteolytically inactivating  Factor V a  and  Factor VIII a , turning them into Factor V i  and Factor VIII i  respectively. When still bound to EPCR, activated protein C performs its cytoprotective effects, acting on the  effector   substrate  PAR-1,  protease-activated receptor-1 . To a degree, APC's anticoagulant properties are independent of its cytoprotective ones, in that expression of one pathway is not affected by the existence of the other. [ 9 ] : 3162  [ 34 ] : 26S


The activity of protein C may be  down-regulated  by reducing the amount either of available thrombomodulin or of EPCR. This may be done by inflammatory  cytokines , such as  interleukin-1β   (IL-1β ) and  tumor necrosis factor-α  (TNF-α). Activated leukocytes release these inflammatory mediators during inflammation, inhibiting the creation of both thrombomodulin and EPCR, and inducing their shedding from the endothelial surface. Both of these actions down-regulate protein C activation. Thrombin itself may also have an effect on the levels of EPCR. In addition, proteins released from cells can impede protein C activation, for example  eosinophil , which may explain thrombosis in  hypereosinophilic  heart disease. [β]  Protein C may be  up-regulated  by  platelet factor 4 . This cytokine is conjectured to improve activation of protein C by forming an  electrostatic bridge  from protein C's Gla domain to the  glycosaminoglycan  (GAG) domain of thrombomodulin, reducing the  Michaelis constant  (K M ) for their reaction. [ 16 ] : 2386  [ 34 ] : 29S   In addition, Protein C is inhibited by  protein C inhibitor . [ 35 ] : 369


Protein C is a major component in anticoagulation in the human body. It acts as a  serine protease   zymogen : APC proteolyses peptide bonds in activated  Factor V  and  Factor VIII  (Factor V a  and Factor VIII a ), and one of the amino acids in the bond is  serine . [ 16 ] : 2381   These proteins that APC inactivates, Factor V a  and Factor VIII a , are highly procoagulant cofactors in the generation of  thrombin , which is a crucial element in blood clotting; together they are part of the  prothrombinase complex . [ 34 ] : 26S   Cofactors in the inactivation of Factor V a  and Factor VIII a  include  protein S , Factor V,  high-density lipoprotein , anionic  phospholipids  and  glycosphingolipids . [ 9 ] : 3161


Factor V a  binds to  prothrombin  and Factor X a , increasing the rate at which thrombin is produced by four orders of magnitude (10,000x). Inactivation of Factor V a  thus practically halts the production of thrombin. Factor VIII, on the other hand, is a cofactor in production of activated Factor X, which in turn converts prothrombin into thrombin. Factor VIII a  augments Factor X activation by a factor of around 200,000. Because of its importance in clotting, Factor VIII is also known as anti-haemophilic factor, and deficiencies of Factor VIII cause  haemophilia A . [ 16 ] : 2382, 3


APC inactivates Factor V a  by making three cleavages (Arg 306 , Arg 506 , Arg 679 ). The cleavages at both Arg 306  and Arg 506  diminish the molecule's attraction to Factor X a , and though the first of these sites is slow to be cleaved, it is entirely necessary to the functioning of Factor V. Protein S aids this process by catalysing the proteolysis at Arg 306 , in which the A2 domain of Factor V is dissociated from the rest of the protein. [ 36 ]  Protein S also binds to Factor X a , inhibiting the latter from diminishing APC's inactivation of Factor V a . [ 16 ] : 2386


The inactivation of Factor VIII a  is not as well understood. The half-life of Factor VIII a  is only around two minutes unless Factor IX a  is present to stabilise it. Some have questioned the significance of APC's inactivation of Factor VIII a , and it is unknown to what degree Factor V and protein S are cofactors in its proteolysis. It is known that APC works on Factor VIII a  by cleaving at two sites, Arg 336  and Arg 562 , either of which is sufficient to disable Factor VIII a  and convert it to Factor VIII i . [ 16 ] : 2387


When APC is bound to EPCR, it performs a number of important cytoprotective (i.e. cell-protecting) functions, most of which are known to require EPCR and PAR-1. These include regulating gene expression, anti-inflammatory effects, antiapoptotic effects and protecting endothelial barrier function. [ 9 ] : 3162


Treatment of cells with APC demonstrates that its gene expression modulation effectively controls major pathways for inflammatory and apoptotic behaviour. There are about 20 genes that are up-regulated by protein C, and 20 genes that are down-regulated: the former are generally anti-inflammatory and antiapoptotic pathways, while the latter tend to be proinflammatory and proapoptotic. APC's mechanisms for altering gene expression profiles are not well understood, but it is believed that they at least partly involve an inhibitory effect on  transcription factor  activity. [ 9 ] : 3162, 4   Important proteins that APC up-regulates include  Bcl-2 ,  eNOS  and  IAP . APC effects significant down-regulation of  p53  and  Bax . [ 16 ] : 2388


APC has anti-inflammatory effects on  endothelial  cells and  leukocytes . APC affects endothelial cells by inhibiting  inflammatory mediator release  and down-regulating  vascular adhesion molecules . This reduces leukocyte adhesion and infiltration into tissues, while also limiting damage to underlying tissue. APC supports endothelial barrier function and reduces  chemotaxis . APC inhibits the release of inflammatory-response mediators in leukocytes as well as endothelial cells, by reducing cytokine response, and maybe diminishing systemic inflammatory response, such as is seen in  sepsis . Studies on both rats and humans have demonstrated that APC reduces  endotoxin -induced pulmonary injury and inflammation. [ 9 ] : 3164


Scientists recognise activated protein C's antiapoptotic effects, but are unclear as to the exact mechanisms by which apoptosis is inhibited. It is known that APC is  neuroprotective . Antiapoptosis is achieved with diminished activation of  caspase 3  and  caspase 8 , improved Bax/Bcl-2 ratio and down-regulation of p53. [ 16 ] : 2388


Activated protein C also provides much protection of endothelial barrier function. Endothelial barrier breakdown, and the corresponding increase in endothelial permeability, are associated with  swelling ,  hypotension  and inflammation, all problems of sepsis. APC protects endothelial barrier function by inducing PAR-1 dependent  sphingosine kinase-1  activation and up-regulating  sphingosine-1-phosphate  with  sphingosine kinase . [ 9 ] : 3165


Several studies have indicated that the proteolytic activity of APC contributes to the observed cytoprotective properties of APC, but variants that are proteolytically inactive also are able to regulate formation of PAR-activators thrombin and factor Xa and express cytoprotective properties in vitro and in vivo. [ 37 ] [ 38 ]


A genetic  protein C deficiency , in its mild form associated with  simple heterozygosity , causes a significantly increased risk of  venous thrombosis  in adults. If a fetus is  homozygous  or  compound heterozygous  for the deficiency, there may be a presentation of  purpura fulminans , severe  disseminated intravascular coagulation  and simultaneous  venous thromboembolism  in the womb; [ 21 ] : 1214    this is very severe and usually fatal. [ 39 ] : 211s   Deletion of the protein C gene in mice causes fetal death around the time of birth. Fetal mice with no protein C develop normally at first, but experience severe bleeding,  coagulopathy , deposition of  fibrin  and  necrosis  of the liver. [ 9 ] : 3161


The frequency of protein C deficiency among asymptomatic individuals is between 1 in 200 and 1 in 500. In contrast, significant symptoms of the deficiency are detectable in 1 in 20,000 individuals. No racial nor ethnic biases have been detected. [ 21 ] : 1215


At least 177 disease-causing mutations in this gene have been discovered. [ 40 ]   Activated protein C resistance  occurs when APC is unable to perform its functions. This disease has similar symptoms to protein C deficiency. The most common mutation leading to activated protein C resistance among Caucasians is at the cleavage site in Factor V for APC. There, Arg 506  is replaced with Gln, producing  Factor V Leiden . This mutation is also called a R506Q. [ 16 ] : 2382   The mutation leading to the loss of this cleavage site actually stops APC from effectively inactivating both Factor V a  and Factor VIII a . Thus, the person's blood clots too readily, and he is perpetually at an increased risk for thrombosis. [ 41 ] : 3   Individuals heterozygous for the Factor V Leiden  mutation carry a risk of venous thrombosis 5–7 times higher than in the general population. Homozygous subjects have a risk 80 times higher. [ 7 ] : 40   This mutation is also the most common hereditary risk for venous thrombosis among  Caucasians . [ 16 ] : 2382


Around 5% of APC resistance are not associated with the above mutation and Factor V Leiden . Other genetic mutations cause APC resistance, but none to the extent that Factor V Leiden  does. These mutations include various other versions of Factor V, spontaneous generation of  autoantibodies  targeting Factor V, and dysfunction of any of APC's cofactors. [ 16 ] : 2387   Also, some acquired conditions may reduce the efficacy of APC in performing its anticoagulative functions. [ 7 ] : 33   Studies suggest that between 20% and 60% of thrombophilic patients suffer from some form of APC resistance. [ 7 ] : 37


Warfarin necrosis  is an acquired protein C deficiency due to treatment with  warfarin , which is a vitamin K antagonist and an anticoagulant itself. However, warfarin treatment may produce paradoxical skin lesions similar to those seen in purpura fulminans. A variant of this response presents as venous limb  gangrene  when warfarin is used to treat deep vein thrombosis associated with cancer. In these situations, warfarin may be restarted at a low dosage to ensure that the protein C deficiency does not present before the vitamin K coagulation factors II, IX and X are suppressed. [ 39 ] : 211s


Activated protein C cleaves  Plasmodium falciparum   histones  which are released during infection: cleavage of these histones eliminates their pro inflammatory effects. [ 42 ]


In November 2001, the  Food and Drug Administration  approved  Drotrecogin alfa-activated  (DrotAA) for the clinical treatment of adults suffering from severe sepsis and with a high risk of death. [ 43 ] : 1332   Drotrecogin alfa-activated is a  recombinant  form of human activated protein C (rhAPC). It is marketed as Xigris by  Eli Lilly and Company , [ 27 ] : 224


Drotrecogin alfa-activated was the subject of significant controversy while it was approved for clinical use as it was found to increase bleeding and not to reduce mortality. [ 44 ] [ needs update ]  In October 2011 rhAPC (Xigris) was withdrawn from the market by Eli Lilly due to a higher mortality in a trial among adults. [ 12 ] [ 44 ]


APC has been studied as way of treating  lung  injury, after studies showed that in patients with lung injury, reduced APC levels in specific parts of the lungs correlated with worse outcomes. [ 9 ] : 3167, 8   APC also has been considered for use in improving patient outcome in cases of  ischemic stroke , a medical emergency in which arterial blockage deprives a region of brain of oxygen, causing tissue death. Promising studies suggest that APC could be coupled with the only currently approved treatment,  tissue plasminogen activator  (tPA), to protect the brain from tPA's very harmful  side effects , in addition to preventing cell death from lack of oxygen ( hypoxia ). [ 45 ] : 211   Clinical use of APC has also been proposed for improving the outcome of  pancreatic islet transplantation  in treating  type I diabetes . [ 16 ] : 2392


Ceprotin was approved for medical used in the European Union in July 2001. [ 46 ]  Ceprotin is indicated in purpura fulminans and coumarin-induced skin necrosis in people with severe congenital protein C deficiency. [ 46 ]


Prothrombin activator  is a complex of a dozen blood coagulation factors that functions in catalyzing  prothrombin  into  thrombin . Prothrombin activator is released in the body by a cascade of chemical reactions in response to damage in a blood vessel.


In  hematology ,  red cell agglutination  or  autoagglutination  is a phenomenon in which  red blood cells  clump together, forming aggregates. It is caused by the surface of the red cells being coated with  antibodies . [ 1 ] : 98   This often occurs in  cold agglutinin disease , a type of  autoimmune hemolytic anemia  in which people produce antibodies (termed cold agglutinins) that bind to their red blood cells at cold temperatures and destroy them. People may develop cold agglutinins from  lymphoproliferative disorders , from infection with  Mycoplasma pneumoniae  or  Epstein–Barr virus , or  idiopathically  (without any apparent cause). Red cell agglutination can also occur in  paroxysmal nocturnal hemoglobinuria [ 2 ] : 13  [ 3 ]  and  warm autoimmune hemolytic anemia . [ 4 ] : 88   In cases of red cell agglutination, the  direct antiglobulin test  can be used to demonstrate the presence of antibodies bound to the red cells. [ 3 ]


Red blood cell aggregates are counted as single cells by the  automated analyzers  used to run  complete blood count  tests. This leads to a markedly decreased  red blood cell  count and  hematocrit  and markedly elevated  mean cell volume  and  mean cell hemoglobin concentration . [ 5 ] : 32–3    Red cell agglutination also interferes with routine methods for  blood typing  and  blood compatibility testing , which rely on agglutination reactions. People with red cell agglutination may exhibit spontaneous agglutination reactions during testing, leading to a false positive result. [ 6 ] : 141, 262   If the causative antibodies are only active at room temperature, the agglutination can be reversed by heating the blood sample to 37 °C (99 °F). People with  warm autoimmune hemolytic anemia  may exhibit red cell agglutination that does not resolve on warming. [ 4 ] : 88


Rheopheresis  is a process to change the viscosity of blood by filtering blood to remove some components such as  fibrinogen ,  alpha-2-macroglobulin ,  von Willebrand factor ,  LDL cholesterol  and  immunoglobulin M . [ 1 ]


It is an experimental treatment for dry  age-related macular degeneration , [ 2 ]  and acute ischemic stroke. [ 3 ]


This  medical treatment –related article is a  stub . You can help Wikipedia by  expanding it .


Riboflavin carrier proteins  (RFCPs) together with  human serum albumin  transport  flavin mononucleotide  (FMN) in the  blood circuit . RFCPs are important in  pregnancy .


Studies from India have identified a riboflavin carrier protein (RCP) present in bird (e.g., chicken) eggs, which is considered to be specific for riboflavin, and is essential for normal embryological development. If this protein is rendered ineffective (e.g., by immuno-neutralization) by treatment of the bird with a specific antibody, then embryonic development ceases and the embryo dies. A genetic mutant lacking RCP is likewise infertile. A homologous protein, which can be rendered ineffective by the antibody to pure chicken riboflavin carrier protein, has been shown to occur in several mammalian species, including two species of monkeys, and also in humans. Very recent studies have suggested that circulating RCP levels and the immunohistochemical staining of RCP in biopsy specimens may provide new markers for  breast cancer diagnosis and prognosis . Termination of pregnancy has been demonstrated by immuno-neutralization of RCP in monkeys. There remains some controversy over the roles of RCP, however, the other, less specific riboflavin binders in blood, including gamma-gobulins, also seem to play an important role. These studies have provided an intriguing example of the role of specific vitamin-transporting mechanisms, designed to ensure that the vitamin needs of the developing embryo will be efficiency met. Further evidence of the special needs of developing embryos has been provided by the demonstration that riboflavin analogs can cause teratogenic changes, even in the absence of any detectable damage to maternal tissues. [ 1 ]


RCP in chicken eggs is in both the  yolk  and  whites . The RCP found in the yolk differs from that of the egg white. The difference in amino acid structure of RCP attributes to the cite of production and the destination of the RCP—the yolk-RCP (made in the  liver ) had 11-13 less amino acid compared to the whites-RCP (made in the  oviducts ). [ 2 ]   [ 3 ]


The concentration of RCP in chickens depends on the concentration of  estradiol  injected and an increased production of RCP can be induced. [ 4 ]


The dependence of RCP production on estrogen enables a potential role in the detection of  breast cancer .  [ 5 ]


Romanowsky staining  is a prototypical  staining  technique that was the forerunner of several distinct but similar stains widely used in  hematology  (the study of blood) and  cytopathology  (the study of diseased cells). Romanowsky-type stains are used to differentiate  cells  for microscopic examination in  pathological  specimens, especially  blood  and  bone marrow  films, [ 1 ]  and to detect parasites such as  malaria  within the blood. [ 2 ] [ 3 ] [ 4 ] [ 5 ]


The staining technique is named after the Russian physician  Dmitri Leonidovich Romanowsky  (1861–1921), who was one of the first to recognize its potential for use as a blood stain. [ 6 ]


Stains that are related to or derived from the Romanowsky-type stains include  Giemsa ,  Jenner ,  Wright ,  Field ,  May–Grünwald ,  Pappenheim  and  Leishman  stains. They differ in protocols and additives and their names are often confused with one another in practice.


The value of Romanowsky staining lies in its ability to produce a wide range of hues, allowing cellular components to be easily differentiated. This phenomenon is referred to as the  Romanowsky effect , or more generally as  metachromasia . [ 7 ]


Eosin part of the stain is responsible for pink-orange hue of  erythrocytes  and granules inside  cytoplasms  of  eosinophilic leukocytes .


In 1891 Romanowsky [ 8 ] [ 9 ] [ 10 ]  developed a stain using a mixture of  eosin  (typically  eosin Y ) and aged solutions of  methylene blue  that formed hues unattributable to the staining components alone: distinctive shades of purple in the  chromatin  of the cell nucleus and within granules in the  cytoplasm  of some  leukocytes . This became known as the Romanowsky effect. [ 11 ] [ 12 ] [ 6 ] [ 13 ] [ 4 ]  Eosin and pure methylene blue alone (or in combination) do not produce the Romanowsky effect, [ 13 ] [ 4 ]  and the active stains which produce the effect are now considered to be  azure B  and eosin. [ 14 ] [ 3 ] [ 13 ]


Romanowsky-type stains can be made from either a combination of pure dyes, or from methylene blue that has been subject to  oxidative   demethylation , which results in the breakdown of methylene blue into multiple other stains, some of which are necessary to produce the Romanowsky effect. [ 15 ] [ 4 ]  Methylene blue that has undergone this oxidative process is known as "polychromed methylene blue". [ 15 ] [ 4 ]  Polychromed methylene blue may contain up to 11 dyes, including  methylene blue ,  azure A , azure B, azure C,  thionine , methylene violet Bernthesen, methyl thionoline and thionoline. [ 4 ]  The exact composition of polychromed methylene blue depends on the method used, and even batches of the stain from the same manufacturer may vary in composition. [ 15 ]


Common method of rapid oxidation uses increasing pH of the solution with  potassium carbonate  and boiling it, which introduces atmospheric  oxygen . [ 16 ]  Other methods have been employed, as well, such as oxidation in acidic medium with  dichromate anion .


Although azure B and eosin have been shown to be the required components to produce the Romanowsky effect, [ 14 ] [ 3 ] [ 13 ]  these stains in their pure forms have not always been used in the formulation of the staining solutions. [ 4 ]  The original sources of azure B (one of the oxidation products of methylene blue) were from polychromed methylene blue solutions, which were treated with oxidizing agents or allowed to naturally age in the case of Romanowsky. [ 3 ] [ 13 ]   Ernst Malachowsky  in 1891 was the first to purposely polychrome methylene blue for use in a Romanowsky-type stain. [ 15 ] [ 17 ]


Wright's stain can be used alone or in combination with the Giemsa stain, which is known as the Wright-Giemsa stain. [ 1 ]  Wright's stain is named after  James Homer Wright  who in 1902 [ 18 ]  published a method using heat to produce polychromed methylene blue, which is combined with eosin Y. [ 19 ] [ 20 ] [ 21 ] [ 1 ]  The polychromed methylene blue is combined with eosin and allowed to precipitate, forming an eosinate which is redissolved in  methanol . [ 4 ]  The addition of Giemsa to Wright's stain increases the brightness of the "reddish-purple" color of the cytoplasmic granules. [ 1 ] [ 21 ]  The Wright's and Wright-Giemsa stains are two of the Romanowsky-type stains in common use in the United States and are mainly used for the staining of blood and bone marrow films. [ 21 ] [ 1 ]


Jenner's stain is used in  microscopy  for  staining   blood smears . The stain is dark blue and results in very observable clearly stained nucleus.


Giemsa stain is composed of "Azure II" and eosin Y with methanol and glycerol as the solvent. [ 15 ]  "Azure II" is thought to be a mixture of azure B (which Giemsa called "azure I") and methylene blue, although the exact composition of "azure I" is considered a trade secret. [ 4 ] [ 15 ]  Comparable formulations using known dyes have been published and are commercially available. Giemsa stain is considered to be the standard stain for detection and identification of the malaria parasite. [ 5 ]


The May-Grünwald-Giemsa is used for the  staining  of slides obtained by  fine-needle aspiration  in a histopathology lab for the diagnosis of tumorous cells.


This method is a combination of May-Grünwald and Giemsa staining.


In 1901  William Leishman [ 22 ]  developed a stain that was similar to Louis Jenner's but with the replacement of pure methylene blue with polychromed methylene blue. [ 19 ] [ 15 ] [ 4 ]  Leishman's stain is prepared from the eosinate of polychromed methylene blue and eosin Y using methanol as the solvent. [ 4 ]


Field stain is used for staining thick blood films in order to discover  malarial  parasites.


Romanowsky-type stains are widely used in the examination of blood, in the form of  blood films , and in the microscopic  examination of bone marrow   biopsies  and aspirate smears. [ 1 ] [ 23 ]  Examination of both blood and bone marrow can be of importance in the diagnosis of a variety of blood diseases. [ 1 ] [ 23 ]  In the United States the Wright and Wright-Giemsa variants of the Romanowsky-type stains are widely used, [ 1 ]  while in Europe Giemsa stain is commonly employed. [ 1 ]


Of the Romanowsky-type stains, the Giemsa stain is especially important in  the detection and identification of malaria parasites in blood samples . [ 5 ] [ 15 ]   Malaria antigen detection tests  are an alternative to the staining and microscopic examination of blood films for the detection of malaria. [ 5 ]


Romanowsky-type stains are also used for the staining of  cytopathologic  specimens such as those produced from  fine-needle aspirates  and  cerebrospinal fluid  from  lumbar punctures . [ 24 ]


Although debate exists as to who deserves credit for this general staining method, popular usage has attributed it to  Dmitri Leonidovich Romanowsky . [ 14 ] [ 17 ] [ 19 ]


In the 1870s  Paul Ehrlich  used a mixture of acidic and basic dyes including  acid fuchsin  (acid dye) and  methylene blue  (basic dye) to examine blood films. [ 25 ] [ 26 ] [ 27 ] [ 28 ] [ 17 ]  In 1888 Cheslav Ivanovich Chenzinsky used methylene blue, but substituted the acid fuchsin used by Ehrlich with eosin. [ 14 ] [ 27 ] [ 28 ]  Chenzinsky's stain combination was able to stain the  malaria  parasite (a member of the  genus   Plasmodium ). [ 28 ] [ 19 ]  Neither Ehrlich's or Chenzinsky's stains produced the Romanowsky effect as the methylene blue they used was not polychromed. [ 17 ]


Dmitri Romanowsky in 1890 published preliminary findings of his blood stain (a combination of aged methylene blue and eosin), including the results when applied to malaria infected blood. [ 6 ]  This use of polychromed methylene blue differentiated Romanowsky's stain (and the subsequent formulations) from those of Ehrlich and Chenzinsky, which lacked the purple hue associated with the Romanowsky effect. [ 17 ]  Romanowsky's 1890 publication did not include a description of how he modified his methylene blue solution, [ 6 ] [ 17 ]  but in his 1891 doctoral thesis he described methylene blue best as used after mold began forming on the surface. [ 6 ] [ 17 ]  Other than the use of an aged methylene blue solution, Romanowsky's stain was based on Chenzinsky's stain technique. [ 17 ]  Romanowsky's use of his method to study the malaria parasite has been attributed to the continued interest in his staining method. [ 26 ]


Ernst Malachowsky  has been credited with independently observing the same stain combination as Dmitri Romanowsky in 1891, [ 6 ] [ 13 ]  although he has also been credited with being the first to do so. [ 17 ] [ 19 ]  Malachowsky was the first to use a deliberately polychromed methylene blue solution, [ 15 ]  which Malachowsky accomplished by the addition of  borax  to the staining mixture. [ 17 ]  Malachowsky is reported to have demonstrated the stain on June 15, 1890, and in the same year to have published a paper "describing his public demonstration". [ 19 ]  Both the Romanowsky and Malachowsky methods were able to stain the  nucleus  and  cytoplasm  of the  malaria   parasite , when until this point the stains used had only colored the cytoplasm. [ 19 ]


In 1899,  Louis Leopold Jenner  developed a more stable version of the methylene blue and eosin stain by collecting the  precipitate  that forms in water-based mixtures and redissolving it in  methanol . [ 28 ] [ 15 ] [ 4 ]  Romanowsky-type stains prepared from the collected precipitates are sometimes known as  eosinates . [ 4 ]  Besides increasing the stability of the stain, the use of methanol in  Jenner's stain  had the effect of  fixing  the blood samples, [ 4 ]  although Jenner's version of the stain does not produce the Romanowsky effect. [ 28 ] [ 19 ] [ 15 ]


Richard May and  Ludwig Grünwald  in 1892 published a version of the stain (now known as the  May–Grünwald stain ) which is similar to the version proposed by Jenner in 1899, and likewise does not produce the Romanowsky effect. [ 28 ] [ 19 ] [ 15 ]


In 1901, both  Karl Reuter  and  William Leishman [ 22 ]  developed stains that combined Louis Jenner's use of alcohol as the solvent and Malachowsky's use of polychromed methylene blue. [ 19 ] [ 15 ] [ 4 ]  Reuter's stain differed from Jenner's in using  ethyl alcohol  instead of methanol, and Leishman's differed from Jenner's by using  eosin B  instead of  eosin Y . [ 19 ] [ 4 ]


James Homer Wright  in 1902 published [ 18 ]  a method using heat to polychrome the methylene blue, which he combined with eosin Y. This technique is known as  Wright's stain . [ 19 ] [ 20 ]


Gustav Giemsa's  name has also become associated with the stain as he is credited with publishing a useful formulation and protocol in 1902. [ 13 ] [ 6 ] [ 26 ]  Giemsa attempted to use combinations of pure dyes rather than polychromed methylene blue solutions which are highly variable in composition. [ 20 ] [ 19 ] [ 15 ]  Giemsa sold the rights to produce his stain, but never fully published details on how he produced it, [ 19 ]  although it is thought that he used a combination of azure B and methylene blue. [ 15 ]  Giemsa published a number of modifications of his stains between 1902 and 1934. In 1904 [ 29 ]  he suggested adding glycerin to his stain, along with the methanol, to increase its stability. [ 23 ] [ 19 ]


Giemsa stain powders produced in Germany were widely used in the United States until the interruption of the supply during  World War I , which caused increased utilization of James Homer Wright's method for polychroming methylene blue. [ 19 ] [ 1 ]


Splenic aspiration  is the removal of fluid from the  spleen , often with the use of a fine-needle. It is rarely practiced in modern medicine. [ 1 ]  It is indicated only in cases of  hypersplenism , or other cases of unexplained  spleen  enlargement. The Moeschlin technique is a common technique for performing a splenic aspiration. There are reports of using this technique in patients with  kala azar .


Streptolysins  are two  homogenous   exotoxins  from  Streptococcus pyogenes . [ 1 ] [ 2 ]  Types include streptolysin O (SLO;  slo ), which is oxygen-labile, and streptolysin S (SLS;  sagA ), which is oxygen-stable. [ 3 ]


SLO is part of the  thiol-activated cytolysin  family. [ 4 ]  It is hemolytically active only in a reversibly reduced state. It is antigenic, so its antibody  antistreptolysin O  can be detected in an  antistreptolysin O titre .


SLS is stable in the presence of oxygen. It is not antigenic due to its small size. It is sometimes considered a  bacteriocin  due to similarities in the synthesis pathway. [ 5 ]


Streptolysin O (SLO;  slo),  is a bacterial toxin that has four  protein domains  which is known to make the plasma membranes in animal cells permeable. It does this by creating pore complexes within the membrane by first binding a monomer to the cholesterol found in the target membrane and then forming an  oligomeric  transmembrane pore. [ 6 ]  This toxin excreted by a  Gram-positive bacteria   Streptococcus pyogenes ,  under the classification of  Thiol-activated cytolysin  or CDCs. In order for Streptolysin O to work effectively, it needs a significant amount of cholesterol to be present in the target membrane. Unlike other  Cholesterol-dependent cytolysins , SLO contains a 60  Amino acid  N-terminal domain that makes it easier to identify.


Human serum albumin  has been demonstrated to neutralize the cytotoxic and hemolytic effects of SLO through its binding in a non-conventional site located in domain II, previously reported to interact also with  C. difficile  toxins. [ 7 ]


This toxin contains highly antigenic effects which causes it to produce the antibody  anti-streptolysin O . Clinically, the presence of these antibodies can indicate a recent  Group A streptococcal infection . Streptolysin O is also known to facilitate apoptosis in  Keratinocytes . It is able to do this by translocating  NAD+ glycohydrolase  (SPN) across the target cells membrane. It then removes the N-terminal domain which stops SPN translocation leading to SPN mediated apoptosis. [ 8 ]


Group A streptococcal infections  are responsible for 517,000 deaths annually across the world. Not much is known about the exact mechanism of action in natural infections however, once the infection is present within the cells it can cause devastating effects. When tested in human endometrium cells, 50% of the cells were killed within the first two hours as a result of processes stimulated by Streptolysin O and SpeB proteases. It has also been observed that both Steptolysin O and SpeB protease limit the innate immune response. [ 9 ]


Streptolysin S (SLS;  sagA ), is a cytolytic  virulence  factor which is a membe of the thiazole/oxadole-modified microcin (TOMM) family. This cytolysin is a  post-translationally modified  peptide was synthesized through a natural evolutionary pathway. SLS is responsible for  Streptococcus pyogenes'   β-hemolytic appearance when grown on blood agar plates. Its biosynthesis is not fully known; however, it is a critical virulence factor for  Streptococcus pyogenes  infections. [ 10 ]  SLS brings about its virulence by damaging soft tissue and it can also act as a signaling molecule. When introduced to a host it will affect its phagocytes and also help to introduce GAS across the skin barrier. [ 11 ]


Streptolysin O (SLO)  is integral to the development of assays designed to detect Anti-Streptolysin O (ASO) antibodies in clinical settings. These assays are critical for diagnosing post-streptococcal diseases, such as acute rheumatic fever and post-streptococcal glomerulonephritis. The SLO antigen, when coupled with latex particles, induces a visible agglutination reaction in the presence of ASO antibodies, allowing for the precise measurement of antibody levels in patient samples.


Superficial vein thrombosis  ( SVT ) is a  blood clot  formed in a  superficial vein , a  vein  near the surface of the body. Usually there is  thrombophlebitis , which is an  inflammatory reaction  around a thrombosed vein, presenting as a painful  induration  (thickening of the skin) with  redness . SVT itself has limited significance (in terms of direct  morbidity  and  mortality ) when compared to a  deep vein thrombosis  (DVT), which occurs deeper in the body at the  deep venous system level . However, SVT can lead to serious complications (as well as signal other serious problems, such as genetic mutations that increase one's risk for clotting), and is therefore no longer regarded as a benign condition. If the blood clot is too near the  saphenofemoral junction  there is a higher risk of  pulmonary embolism , a potentially life-threatening complication.


SVT has risk factors similar to those for other thrombotic conditions and can arise from a variety of causes. Diagnosis is often based on symptoms. There are multiple possible treatments, with the goal of providing symptomatic relief and preventing complications.


SVT is recognized by the presence of pain, warmth, redness, and tenderness over a superficial vein. [ 1 ]  The SVT may present as a "cord-like" structure upon palpation. [ 1 ]  The affected vein may be hard along its entire length. [ 2 ]  SVTs tend to involve the legs, though they can affect any superficial vein (e.g. those in the arms). [ 1 ]


SVT in the lower extremities can lead to a dangerous complication in which the clot travels to the lungs, called  pulmonary embolism  (PE). [ 3 ]  This is because lower limb SVTs can migrate from superficial veins into deeper veins. [ 3 ]  In a French population, the percent of people with SVTs that also suffered from PEs was 4.7%. [ 3 ]  In the same population,  deep vein thrombosis  (DVT) was found in 24.6% of people with SVTs. [ 3 ]  However, because superficial veins lack muscular support, any clots that form are far less likely to be squeezed by muscle contraction, dislodged, and induce a PE. [ 2 ]


SVTs can recur after they resolve, which is termed "migratory thrombophlebitis." [ 2 ]  Migratory thrombophlebitis is a complication that may be due to more serious disorders, such as cancer and other hypercoagulable states. [ 2 ] [ a ]


SVTs of the legs are often due to  varicose veins , though most people with varicose veins do not develop SVTs. [ 2 ]  SVTs of the arms are often due to the placement of intravenous catheters. [ 2 ]


Many of the risk factors that are associated with SVT are also associated with other thrombotic conditions (e.g. DVT). These risk factors include age,  cancer , history of  thromboembolism ,  pregnancy , use of  oral contraceptive  medications (containing estrogen), [ 4 ]   hormone replacement therapy , recent surgery, and certain  autoimmune diseases  (especially  Behçet's  and  Buerger's  diseases). [ 3 ]  Other risk factors include immobilization (stasis) and  laparoscopy . [ 1 ]


Hypercoagulable states  due to genetic conditions that increase the risk of clotting may contribute to the development of SVT, such as  factor V Leiden ,  prothrombin 20210A  mutation, and  protein C ,  S , and  antithrombin III  and  factor XII deficiency . [ 1 ]


The mechanism for the development of an SVT depends upon the specific etiology of the SVT. For example, varicose veins and prolonged bed rest both may induce SVTs due to slowing the flow of blood through superficial veins. [ 1 ]


SVTs may be diagnosed based upon clinical criteria by a healthcare professional. [ 1 ]  A more specific evaluation can be made by  ultrasound . [ 1 ]  An ultrasound can be useful in situations in which an SVT occurs above the knee and is not associated with a varicose vein, because ultrasounds can detect more serious clots like DVTs. [ 2 ]  The diagnostic utility of  D-dimer  testing in the setting of SVTs has yet to be fully established. [ 3 ]


SVTs can be classified as either  varicose vein  (VV) or non-varicose (NV) associated. [ 1 ]  NV-SVTs are more likely to be associated with genetic procoagulable states compared to VV-SVTs. [ 1 ]  SVTs can also be classified by  pathophysiology . That is, primary SVTs are characterized by inflammation that is localized to the veins. Secondary SVTs are characterized by systemic inflammatory processes. [ 1 ]


A subclass of SVTs are  septic thrombophlebitis , which are SVTs that occur in the setting of an infection. [ 5 ]


The goal of treatment in SVT is to reduce local inflammation and prevent the SVT from extending from its point of origin. [ 1 ]  Treatment may entail the use of compression, physical activity, medications, or surgical interventions. [ 1 ]  The optimal treatment for many SVT sites (i.e. upper limbs, neck, abdominal and thoracic walls, and the penis) has not been determined. [ 3 ]


Multiple compression bandages exist. Fixed compression bandages, adhesive short stretch bandages, and graduated elastic  compression stockings  have all be used in the treatment of SVTs. [ 1 ]  The benefit of compression stockings is unclear, though they are frequently used. [ 3 ]


Inactivity is contraindicated in the aftermath of an SVT. [ 1 ]  Uninterrupted periods of sitting or standing may cause the SVT to elongate from its point of origin, increasing the risk for complications and clinical worsening. [ 1 ]


Medications used for the treatment of SVT include  anticoagulants ,  NSAIDs  (except  aspirin ),  antibiotics , and  corticosteroids . [ 1 ]


SVTs that occur within the  great saphenous vein  within 3 cm of the  saphenofemoral junction  are considered to be equivalent in risk to DVTs. [ 3 ]   These high risk SVTs are treated identically with therapeutic anticoagulation. [ 3 ]  Anticoagulation is also used for intermediate risk SVTs that are greater than 3 cm from the saphenofemoral junction or are greater than 4–5 cm in length. [ 3 ]


Anticoagulation for high risk SVTs includes the use of  vitamin K antagonists  or  novel oral anticoagulants (NOACs)  for 3 months. [ 3 ]  Anticoagulation for intermediate risk SVTs includes  fondaparinux  2.5 mg daily for 45 days or the use of intermediate to therapeutic dose  low molecular weight heparin  for 4–6 weeks. [ 3 ]


NSAIDs  (non-steroidal anti-inflammatory drugs) can be used in both oral or topical formulations for the relief of SVT symptoms. [ 3 ]  The British Committee for Standards in Haematology guidelines recommend the use of NSAIDs for low-risk SVTs (thrombus <4–5 cm in length, no additional risk factors for thromboembolic events). [ 3 ]  NSAIDs are used for treatment durations of 8–12 days. [ 3 ]


Antibiotics are used in the treatment of  septic SVT . [ 1 ]   Corticosteroids  are used for the treatment of SVTs in the setting of vasculitic and autoimmune syndromes. [ 1 ]


Surgical interventions are used for both symptomatic relief of the SVT as well as for preventing the development of more serious complications (e.g. pulmonary embolism). [ 3 ]  Surgical interventions include  ligation  of the saphenofemoral junction, ligation and  stripping  of the affected veins, and local  thrombectomy . [ 3 ]  Because of the risk of symptomatic pulmonary embolism with surgery itself, surgical interventions are not recommended for the treatment of lower limb SVTs by the 2012  American College of Chest Physicians  guidelines and the 2012  British Committee for Standards in Haematology  guidelines. [ 3 ]  The use of surgery for the treatment of SVT is controversial. [ 6 ]


SVT is often a mild, self-resolving medical condition. [ 1 ]  The inflammatory reaction may last up to 2–3 weeks, with possible recanalization of the thrombosed vein occurring in 6–8 weeks. [ 1 ]  The superficial vein may continue to be hyperpigmented for several months following the initial event. [ 1 ]


In a French population, SVT occurred in 0.64 per 1000 persons per year. [ 3 ]


SVTs have been historically considered to be benign diseases, for which treatment was limited to conservative measures. [ 6 ]  However, an increased awareness of the potential risks of SVTs developing into more serious complications has prompted more research into the diagnosis, classification, and treatment of SVTs. [ 6 ]


A Cochrane review recommends that future research investigate the utility of oral, topical, and surgical treatments for preventing the progression of SVTs and the development of thromboembolic complications. [ 7 ] [ 8 ]


Tamponade  ( / ˌ t æ m . p ə ˈ n eɪ d / [ 1 ] ) is the closure or blockage (as of a wound or body cavity) by or as if by a  tampon , especially to stop bleeding. [ 2 ]
Tamponade is a useful method of stopping a  hemorrhage . This can be achieved by applying an absorbent dressing directly into a wound, thereby absorbing excess blood and creating a blockage, or by applying direct pressure with a hand or a  tourniquet .
Not to be confused with a tamponade that occurs as a result of health problems. For example:  cardiac tamponade  is a condition where fluid collects in the  pericardial sac  increasing pressure within the pericardium which in turn prevents the  ventricles  from expanding fully significantly reducing the efficiency of the heart. It is considered a medical emergency and if left unchecked is fatal.


Bladder tamponade  is obstruction of the  urinary bladder  outlet due to heavy  blood clot  formation within it. [ 3 ]  It generally requires surgery. [ 3 ]  Such heavy bleeding is usually due to  bladder cancer . [ 4 ]


Pressing  bone wax  into bleeding bone is considered hemostasis by tamponade, as opposed to methods which physically or biochemically activate the clotting cascade.


Gas tamponade has been used  for  retinal detachment  surgery, helping reduce the rate of fluid flow through retinal tears. Research suggests that patients undergoing surgery with tamponade agents of  C 3 F 8  gas and standard silicone oil had the best visual and anatomic outcomes, over other tamponade agents. [ 5 ]


THP-1  is a human  monocytic   cell line  derived from an  acute monocytic leukemia  patient. It is used to test  leukemia  cell lines in  immunocytochemical  analysis of protein-protein interactions, and  immunohistochemistry . [ 1 ]


Although THP-1 cells are of the same lineage, mutations can cause differences as the progeny proliferates. In general, THP-1 cells exhibit a large, round, single-cell morphology. The cells were derived from the peripheral blood of a 1-year-old human male with acute monocytic leukemia. Some of their characteristics are: [ 1 ]


THP-1 can provide continuous culture when grown in suspension;  RPMI  1640 + 10% FBS + 2mM L-Glutamine. The average doubling time is 19 to 50 hours.
1 mM sodium pyruvate, penicillin (100 units/ml) and streptomycin (100 μg/ml) are also commonly added to inhibit bacterial contamination. Cultures should be maintained at cell densities in the range 2-9x10 5  cells/ml at 37 °C, 5% CO 2 . Cells are non-adherent. [ 5 ]


THP-1 cells are of human origin, and no evidence has been found for the presence of infectious viruses or toxic products. The ATCC Biosafety recommendation is level 1. [ 5 ]


THP-1 cells are used as a models to study the monocyte-macrophage differentiation process, [ 6 ]  antigen presentation [ 7 ] [ 8 ]  and as a model to examine some macrophage-related physiological processes, for example the macrophage cholesterol efflux. [ 9 ]


Thromboembolism  is a condition in which a blood clot ( thrombus ) breaks off from its original site and travels through the bloodstream (as an  embolus ) to obstruct a blood vessel, causing tissue  ischemia  and organ damage. Thromboembolism can affect both the venous and arterial systems, with different clinical manifestations and management strategies. [ 2 ] [ 3 ]


Venous thromboembolism (VTE)  BD72  comprises the following conditions: [ 3 ] [ 4 ] [ 5 ]


VTE is a common cardiovascular disorder with significant  morbidity  and mortality. [ 3 ] [ 4 ] [ 5 ]  VTE can present with various symptoms, such as painful leg swelling, chest pain,  dyspnea ,  hemoptysis ,  syncope , and even death, depending on the location and extent of the thrombus. [ 4 ] [ 6 ]  VTE can also cause long-term complications, such as recurrent VTE, post-PE syndrome, chronic thromboembolic pulmonary hypertension (CTEPH), and post-thrombotic syndrome (PTS). The mainstay of VTE management is anticoagulation therapy, which prevents thrombus propagation and embolization. Such treatment reduces the risk of recurrence. [ 5 ] [ 4 ] [ 1 ]  The choice and duration of anticoagulation depend on the individual patient's risk factors, bleeding risk, and preferences.  Direct oral anticoagulants  (DOACs) have emerged as an essential alternative to conventional anticoagulants, such as  vitamin K antagonists  (VKAs) and  low-molecular-weight heparins  (LMWHs), due to their rapid onset of action, predictable pharmacokinetics, fixed dosing, and lower risk of bleeding. DOACs can also facilitate home treatment and extended therapy for selected patients. In addition to anticoagulation, some patients with VTE may benefit from adjunctive therapies, such as  thrombolysis , catheter-directed interventions, or  inferior vena cava (IVC) filters , to remove or prevent thrombus migration. However, these therapies are associated with higher risks of bleeding and complications. These therapies are not routinely recommended by the current guidelines except for specific indications, such as massive PE, iliofemoral DVT, or contraindications to anticoagulation. The optimal duration of anticoagulation for VTE is determined by the balance between the risk of recurrence and the risk of bleeding, and should be individualized for each patient. In general, VTE provoked by a transient or reversible risk factor, such as surgery, trauma, or immobilization, should be treated for three months, while VTE provoked by a persistent or progressive risk factor, such as cancer, should be treated indefinitely. Unprovoked VTE, which occurs in the absence of any identifiable risk factor, has a high risk of recurrence and may require indefinite anticoagulation, depending on the patient's characteristics and preferences. [ 4 ] [ 7 ] [ 8 ]  Factors that favor indefinite anticoagulation include male sex, presentation as PE (especially with concomitant DVT), positive d-dimer test after stopping anticoagulation, presence of antiphospholipid antibodies, low bleeding risk, and patient preference. [ 3 ]  The type of anticoagulant used for indefinite therapy is of secondary importance, but low-dose DOACs may offer a convenient and safer option for some patients. [ 4 ] [ 7 ] [ 8 ]  For cancer-associated VTE, full-dose DOACs are now preferred over LMWHs, unless there are gastrointestinal lesions that increase the risk of bleeding. [ 4 ] [ 7 ] [ 8 ]   Graduated compression stockings  are elastic garments that apply a gradient of pressure to the lower limbs, reducing venous stasis and improving blood flow, still these stockings are not routinely indicated after DVT, but may be helpful if there is persistent leg swelling or symptomatic improvement with a trial of stockings. [ 3 ] [ 9 ]  Medications, such as  pentoxifylline , have a limited role in the treatment of PTS. After PE, patients should be monitored for signs and symptoms of CTEPH, which is a rare but serious complication of VTE. [ 4 ] [ 7 ] [ 8 ]  Ventilation-perfusion scanning and echocardiography are the initial diagnostic tests for CTEPH, and patients with confirmed or suspected CTEPH should be evaluated for potential treatments, such as  pulmonary thromboendarterectomy ,  balloon pulmonary angioplasty , or vasodilator therapies. [ 3 ]


Arterial thromboembolism  (ATE) is a less common but more severe form of thromboembolism, which can affect various organs, such as the brain, heart, kidneys, limbs, and mesentery. ATE can cause life-threatening conditions, such as stroke, myocardial infarction, acute kidney injury, limb ischemia, and mesenteric ischemia. ATE is usually caused by  atherosclerosis , which leads to plaque rupture and thrombus formation, or by cardioembolism, which results from the embolization of a cardiac thrombus, such as in atrial fibrillation, valvular disease, or myocardial dysfunction. The management of ATE depends on the location and severity of the ischemia and the underlying etiology. The main goals of ATE management are to restore blood flow, prevent further thrombosis, and treat the underlying cause. The treatment options for ATE include antithrombotic therapy, revascularization procedures, and risk factor modification. Antithrombotic therapy consists of antiplatelet agents, such as aspirin or clopidogrel, or anticoagulants, such as heparin or DOACs, depending on the indication and contraindications. Revascularization procedures include thrombolysis, thrombectomy, angioplasty, stenting, or bypass surgery and are indicated for patients with severe or limb-threatening ischemia or failed medical therapy. Risk factor modification involves lifestyle changes, such as smoking cessation, exercise, and diet, and pharmacological interventions, such as statins, antihypertensives, and glucose-lowering agents, to reduce the risk of recurrent ATE and improve the prognosis. The duration of antithrombotic therapy for ATE is variable, depending on the type and location of the thrombus, the presence of a prosthetic device, and the bleeding risk. In general, patients with ATE receive lifelong antiplatelet therapy unless there is a specific indication or contraindication for anticoagulation. [ 2 ] [ 10 ]


Property of a  material  (or substance) that induces and/or promotes the formation of a thrombus. [ 1 ]


Thrombogenicity  refers to the tendency of a material in contact with the blood to produce a  thrombus , or clot.  It not only refers to fixed thrombi but also to emboli, thrombi which have become detached and travel through the bloodstream.  Thrombogenicity can also encompass events such as the activation of immune pathways and the  complement system .  All materials are considered to be thrombogenic [ citation needed ]  with the exception of the normal state of  endothelial cells  which line  blood vessels . [ 2 ]   Certain medical implants appear non-thrombogenic due to high flow rates of blood past the implant, but in reality all are thrombogenic to a degree. Various  surface treatments  are available to minimize these thrombogenic effects.


A thrombogenic implant will eventually be covered by a fibrous capsule, the thickness of this capsule can be considered one measure of thrombogenicity, and if extreme can lead to the failure of the implant.


Thromboregulation  is the series of mechanisms in how a primary clot is regulated. These mechanisms include, competitive inhibition or negative feedback. It includes primary  hemostasis , which is the process of how blood platelets adhere to the endothelium of an injured blood vessel. [ 1 ] [ 2 ]   Platelet  aggregation is fundamental to repair vascular damage and the initiation of the blood thrombus formation. The elimination of clots is also part of thromboregulation. Failure in platelet clot regulation may cause hemorrhage or thrombosis. Substances called thromboregulators control every part of these events. [ 3 ]


One primary function of thromboregulation is the control of primary  hemostasis , which is the platelet aggregation process. Some thromboregulators enhance platelet aggregation and some others inhibit the process. Platelet aggregation plays a critical role in the genesis of a resulting  thrombus . Adhesion should remain local, but platelet aggregation must grow exponentially to form a platelet thrombus and prevent blood loss. Platelet aggregation factors are the regulators that enhance the adhesion and stimulate the platelets to secrete its granules. It has been shown that collagen, exposed after the injury to the endothelial cover of the vessel, plays as an agonist in platelet adhesion and its activation. The binding of platelets to the sub-endothelial collagen stimulates the secretion of  ADP ,  TXA2 , and  serotonin  present in the platelet granules. [ 4 ]


ADP-dependent aggregation is mediated by two receptors: the purinergic  P2Y1 , coupled to Gαq, mediates the shape in the structure of platelets and triggers the aggregation process. [ 5 ]   Thromboxane A2  (TX2) has a positive feedback in platelet activation. It is produced by the oxygenation of arachidonic acid by two enzymes:  cycloxygenase  and thromboxane A2 synthase. TX2 effects are mediated by G protein-coupled receptors, subtypes TPα and TPβ. Both receptors mediate  phospholipase C  stimulation causing an increase of intracellular levels of  inositol 1,4,5-triphosphate  and  diacylglycerol . Inositol 1,4,5-triphosphate causes an increase in Ca concentration and the release of diacylglycerol activates  PKC . TPα stimulates cAMP levels whereas TPβ inhibits the level of intracellular cAMP. [ 6 ]  Serotonin, 5-HT, is an amine synthesized in the gut and it is released into the bloodstream after the activation of presynaptic neurons or  enterochromaffin cells  stimulation. Later, it is sequestered by the platelets using antidepressant-sensitive 5-HT transporters (SERTs) and into platelet’s granules by the  vesicular monoamine transporter  (VMAT).  After the secretion, 5-HT increases the effects of prothrombotic agents by its binding with 5-HT2 receptors  [ 7 ]


Thromboregulation is also in charge of regulating the process of clot elimination, called primary hemostasis inhibition. These inhibitors are substances that prevent the clot formation by preventing platelet adhesion. Platelet inhibition is important to prevent thrombotic episodes or the formation of blood clot and consequently preventing heart attacks and strokes. Some primary hemostasis inhibitors are cAMP, prostacyclin,  PGE1 , and kistrin.  cAMP,  cyclic adenosine monophosphate , phosphorylate messengers via protein kinase A (PKA). These signaling elements include  thromboxane A2 , receptor type α, phospholipase Cβ3, and IP3 receptors. Signalization in platelets is very sensitive in cAMP levels. [ 8 ] [ 9 ]   Nitric oxide  (NO) stimulates cGMP production and therefore the activation  cGMP-dependent protein kinase  (G kinase). This kinase inhibits Gαq-phospholipase C-inositol 1,4,5-triphosphate signaling and the mobilization of calcium inside the cell for thromboxane A2. [ 10 ]   PGI2,  prostacyclin , binds to IP receptors that catalyze cAMP formation. This process is mediated via GTP-binding protein Gs and  adenylyl cyclase .  PGE1  binds to IP receptors. IP receptors bind with  ionophores  that induce ADP and serotonin secretion. PGE1 inhibits the secretion of factors that stimulate platelet aggregation by competitive inhibition. [ 11 ] [ 12 ]  Kistrin is a protein inhibitor of platelet aggregation. It belongs to the homologous family of glycoprotein IIb-IIa antagonists. Kistrin has an adhesion site that binds to GP IIb-IIIa. [ 13 ]


Thrombosis  (from  Ancient Greek     θρόμβωσις  (thrómbōsis)  'clotting') is the formation of a  blood clot  inside a  blood vessel , obstructing the flow of  blood  through the  circulatory system . When a blood vessel (a  vein  or an  artery ) is injured, the body uses  platelets  (thrombocytes) and  fibrin  to form a  blood clot  to prevent blood loss.  Even when a blood vessel is not injured, blood clots may form in the body under certain conditions. A clot, or a piece of the clot, that breaks free and begins to travel around the body is known as an  embolus . [ 1 ] [ 2 ]


Thrombosis may occur in  veins  ( venous thrombosis ) or in  arteries  ( arterial thrombosis ). Venous thrombosis (sometimes called DVT,  deep vein thrombosis ) leads to a blood clot in the affected part of the body, while arterial thrombosis (and, rarely, severe venous thrombosis) affects the blood supply and leads to damage of the tissue supplied by that artery ( ischemia  and  necrosis ). A piece of either an arterial or a venous thrombus can break off as an  embolus , which could then travel through the circulation and lodge somewhere else as an  embolism . This type of embolism is known as a  thromboembolism . Complications can arise when a venous thromboembolism (commonly called a VTE) lodges in the lung as a  pulmonary embolism . An arterial embolus may travel further down the affected blood vessel, where it can lodge as an embolism. [ citation needed ]


Thrombosis is generally defined by the type of blood vessel affected (arterial or venous thrombosis) and the precise location of the blood vessel or the organ supplied by it. [ citation needed ]


Deep vein thrombosis (DVT) is the formation of a blood  clot  within a  deep vein . It most commonly affects leg veins, such as the  femoral vein .


Three factors are important in the formation of a blood clot within a deep vein—these are:


Classical signs of DVT include  swelling , pain and redness of the affected area. [ 3 ]


Paget-Schroetter disease  or upper extremity DVT (UEDVT) is the obstruction of an  arm  vein (such as the  axillary vein  or  subclavian vein ) by a thrombus. The condition usually comes to light after vigorous exercise and usually presents in younger, otherwise healthy people. Men are affected more than women. [ 4 ]


Budd-Chiari syndrome  is the blockage of a  hepatic vein  or of the hepatic part of the  inferior vena cava . This form of thrombosis presents with  abdominal pain ,  ascites  and  enlarged liver . Treatment varies between therapy and surgical intervention by the use of  shunts . [ 5 ]


Portal vein thrombosis affects the  hepatic portal vein , which can lead to portal  hypertension  and reduction of the blood supply to the  liver . [ 6 ]  It usually happens in the setting of another disease such as  pancreatitis ,  cirrhosis ,  diverticulitis  or  cholangiocarcinoma . [ 7 ]


Renal vein thrombosis is the obstruction of the  renal vein  by a thrombus. This tends to lead to reduced drainage from the  kidney . [ 8 ]


Cerebral venous sinus thrombosis (CVST) is a rare form of  stroke  which results from the blockage of the  dural venous sinuses  by a thrombus. Symptoms may include headache, abnormal vision, any of the symptoms of stroke such as weakness of the face and limbs on one side of the body and  seizures . The diagnosis is usually made with a  CT  or  MRI scan . The majority of persons affected make a full recovery. The  mortality rate  is 4.3%. [ 9 ]


Jugular vein  thrombosis is a condition that may occur due to infection, intravenous drug use or malignancy. Jugular vein thrombosis can have a varying list of complications, including:  systemic sepsis ,  pulmonary embolism , and  papilledema . Though characterized by a sharp pain at the site of the vein, it can prove difficult to diagnose, because it can occur at random. [ 10 ]


Cavernous sinus thrombosis  is a specialised form of cerebral venous sinus thrombosis, where there is thrombosis of the  cavernous sinus  of the basal skull dura, due to the retrograde spread of infection and endothelial damage from the  danger triangle  of the face. The facial veins in this area anastomose with the  superior  and  inferior  ophthalmic veins of the orbit, which drain directly posteriorly into the cavernous sinus through the  superior orbital fissure .  Staphyloccoal  or  Streptococcal  infections of the face, for example nasal or upper lip pustules may thus spread directly into the cavernous sinus, causing stroke-like symptoms of  double vision ,  squint , as well as spread of infection to cause  meningitis . [ 11 ]


Arterial thrombosis is the formation of a thrombus within an  artery . In most cases, arterial thrombosis follows rupture of  atheroma  (a fat-rich deposit in the blood vessel wall), and is therefore referred to as  atherothrombosis .  Arterial embolism  occurs when clots then migrate downstream and can affect any organ. [ 12 ]  Alternatively, arterial occlusion occurs as a consequence of embolism of blood clots originating from the heart ("cardiogenic" emboli). The most common cause is  atrial fibrillation , which causes a blood stasis within the atria with easy thrombus formation, but blood clots can develop inside the heart for other reasons too as infective endocarditis. [ citation needed ]


A stroke is the rapid decline of brain function due to a disturbance in the supply of blood to the brain. [ 13 ]  This can be due to  ischemia , thrombus,  embolus  (a lodged particle) or  hemorrhage  (a bleed). [ 13 ]


In thrombotic stroke, a thrombus (blood clot) usually forms around  atherosclerotic  plaques. Since blockage of the artery is gradual, the onset of symptomatic thrombotic strokes is slower. Thrombotic stroke can be divided into two categories — large vessel disease or small vessel disease. The former affects vessels such as the  internal carotids ,  vertebral  and the  circle of Willis . The latter can affect smaller vessels, such as the branches of the circle of Willis. [ citation needed ]


Myocardial infarction (MI), or heart attack, is caused by ischemia (restriction in the blood supply), which is often due to the obstruction of a  coronary artery  by a thrombus. This restriction gives an insufficient supply of oxygen to the heart muscle which then results in tissue death (infarction). A lesion is then formed which is the  infarct . MI can quickly become fatal if emergency medical treatment is not received promptly. If diagnosed within 12 hours of the initial episode (attack) then  thrombolytic therapy  is initiated. [ citation needed ]


An arterial thrombus or embolus can also form in the limbs, which can lead to  acute limb ischemia . [ 14 ]


Hepatic artery thrombosis  usually occurs as a devastating complication after  liver transplantation . [ 15 ]