Transfusion Medicine Glossary

The A1 antigen is seen in 80% of individuals who type A or AB, while the remaining 20% of patients are usually type A2, and a small minority are other weaker subgroups (<0.1%). Anti-A1 antibodies are naturally occurring IgM cold agglutinins, and are seen in 1-8% of type A2 individuals, and 22-35% of the A2B individuals. Anti-A1 antibodies typically do not cause hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN). However, when the antibody is reactive at 37 degrees C, hemolysis has been reported.

Acronym for the American Association of Blood Banks. AABB is a non-profit organization centered around the science and practice of transfusion medicine, including blood component therapy and blood donation. AABB can accredit hospital blood banking programs and assist with their compliance of federal regulations.

Refers to a specific antigen system located on red blood cells (RBCs) and platelets (e.g. blood type A, B, AB or O). ABO blood type determination is an essential part of pre-transfusion testing for patients. (Note: Patients with type A RBCs will have type B antibody in their plasma, while patients with type B RBCs will have type A antibody in their plasma. Since type O patient's red blood cells lack A and B antigens, then not surprisingly they could have antibodies to both A and B antigens in their plasma. On the other hand, AB patients plasma is typically devoid of antibodies to either A or B antigen. Hence, the universal donor for RBCs is type O (devoid of A or B antigens) and universal donor for plasma is type AB (devoid of anti-A or Anti-B anti antibodies).

Also abbreviated as aPTT. An in vitro assay for evaluating the intrinsic (and common) pathway of coagulation which involves mixing and incubating the patient's plasma with phospholipid; calcium chloride is then added and the time it takes for a clot to form is measured.

Rapid depletion of blood primarily from the intravascular space. When criteria are met for a specific volume of blood lost within a span of time, a massive transfusion protocol may be warranted.

B lymphocyte-mediated response to extracellular microorganisms and foreign substances carried out by the immunoglobulins (antibodies) and other products they secrete.

Also known as ADA deficiency. A specific enzyme deficiency known to cause an autosomal recessive form of severe combined immunodeficiency disease (SCID). Those afflicted with ADA deficiency may have various skeletal abnormalities in addition to a severe reduction in B and T lymphocytes and natural killer (NK) cells, which would result in death from opportunistic infection if left untreated. Enzyme replacement therapy and bone marrow transplants have been used as treatment.

A major protein constituent of blood plasma. This protein is relatively negatively charged (as opposed to immunoglobulins which are relatively positively charged) and serves as a major protein in the plasma. It is produced in the liver so levels are usually reduced in end stage liver disease.

These are antibodies that recognize non-self antigens. An example: Alloantibodies can develop in patients who have received prior transfusions. Hence, having formed antibodies to non-self red blood cell antigens (e.g. anti-Kell, etc.). If a patient develops an alloantibody to Kell positive RBCs, the next time this patient receives a Kell positive RBC transfusion, he or she may adversely react to the transfused blood and develop a hemolytic transfusion reaction which could be fatal. This is a major reason for testing patient's blood prior to transfusing them with blood products.

Potentially life-threatening type I hypersensitivity reaction involving mast cell degranulation and manifested by urticaria, angioedema, respiratory distress, and gastrointestinal symptoms. In the context of transfusion medicine, anaphylactic (anaphylactoid) reactions occur when donor plasma in a blood component is transfused to a recipient with preformed antibodies. This is often seen in recipients who are IgA deficient.

Refers to a decrease in hematocrit/hemoglobin levels (e.g. iron deficiency anemia). Anemias are typically classified into 3 broad categories: microcytic anemia (MCV <80), normocytic anemia (MCV 80-100) and macrocytic anemia (MCV >100).

Antibody formed against one of the antigens that comprise part of the RhCE protein. Because of genetic linkage, anti-c is frequently found along with anti-E. The c antigen belongs to the Rh antigen system. Anti-c antibodies are usually formed in response to transfusion or pregnancy. Anti-c antibodies are clinically significant and can cause acute or delayed hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN) if the patient is challenged with antigen positive blood.

Antibody formed to one of the Rh antigens on red blood cells known as D antigen which can lead to red blood cell destruction. A classic example of this is seen in hemolytic disease of the newborn where the mother's anti-D antibodies attack and destroy the fetal Rh (D) positive red blood cells.

Antibody with reactivity that would suggest a compound antibody to both C and D which must be distinguished from true anti-D so that RhIg can be administered, especially in the obstetrical patient.

Antibody formed against a glycoprotein antigen from a clinically important (strongly immunogenic) blood group system. Antibodies to Kell antigens can be associated with hemolytic disease of the fetus and newborn (HDFN) as well as hemolytic transfusion reactions (HTRs). It is present on the red blood cells of ~9% of white, ~2% of black and rare in East Asian patients.

A protein that is produced by B cells (in terminally differentiated B-cells known as plasma cells, these immunoglobulins are produced and secreted and are not cell surface bound) which recognize and bind to other proteins or substances (foreign or self antigens). Antibodies can be part of an immune response and help eradicate viruses and bacteria or may be part of an autoimmune destructive process in hematology such as autoimmune hemolytic anemia or immune mediated platelet destruction (e.g. ITP).

Process of determining which antibody is causing a positive antibody screen ordered for a patient who may need a blood transfusion. After an antibody screen (IAT or indirect antiglobulin test) is found to be positive (i.e., causes agglutination), antibody identification is conducted to determine whether the offending antibody is an alloantibody, autoantibody, or both. Reagent red blood cells with known phenotypes are tested with the patient's serum as well an an autocontrol, and the presence of agglutination is noted. The panels are interpreted by a blood bank technician or technologist or pathologist and the identified antibody is recorded in the patient's medical record. If a transfusion is required, compatible blood is supplied based on those results.

Assay or method which detects antibodies toward non-ABO blood group antigens, primarily alloantibodies such as Kell, Kidd, etc. It tests the patient's serum with reagent red blood cells with known antigens attached to them. An antibody screen is done prior to every blood transfusion to identify which unit(s) of blood will be least likely to cause an antibody response from the recipient of the transfusion.

These are natural or synthetic compounds that prevent the formation of blood clots. Common examples include heparin, warfarin (coumadin), etc.

Typically refers to a molecular structure (on a foreign substance or self) which can be recognized by an antibody (e.g. foreign antigens include viral and bacterial components while self-antigens include certain aspects of a platelet or red blood cell, etc.).

A catch-all term for the process whereby a person's blood is circulated through a machine (an apheresis unit) and separated into its component parts, with certain components being collected and the rest being returned into circulation. Depending on the many uses of apheresis--therapeutic, blood donation, etc.--the component(s) removed from the person's circulation and returned vary. For example, a platelet donor will have a portion of his/her total platelets removed from circulation so they can be later used for platelet transfusion for someone else. In a therapeutic scenario, a person with a dangerously high white blood cell count may have a portion of only his white blood cells removed and the remainder returned.

An antibody (a specific type of protein) manufactured by the immune system that is directed against one or more of the individual's own proteins. Autoantibodies can be detected with an antibody screening procedure. These are not a normal occurrence and may indicate autoimmune hemolytic anemia. The autocontrol tube within the antibody screening will detect this type of antibody and other causes of a positive direct antiglobulin test (DAT).

Also known as AIHA. This is an autoantibody-mediated red blood cell destruction caused by warm (IgG-mediated) or cold (IgM-mediated) antibodies. Warm autoantibodies activate destruction through macrophages, whereas cold antibodies elicit the complement system. Causes of AIHA include viral infections, autoimmune disorders, certain lymphomas, and medications. It can also be idiopathic.

Transfusion of a person's own blood or blood components. It is most commonly used when someone with a scheduled surgery banks his/her own blood days before the procedure, primarily to reduce the risk of certain infection or incompatibility associated with an allogeneic (non-self) transfusion.

Also known as a weak B phenotype or B subgroup. Individuals with one of these rare variations of a B blood type which may show weaker than expected serologic activity and may cause an ABO typing discrepancy.

Adverse transfusion-associated reactions can occur with bacterial contamination of blood components. Most often bacterial contamination affects red blood cell concentrates and platelet concentrates. The bacterium most commonly responsible for sepsis associated with red blood cell concentrate transfusion is Yersinia enterocolitica. In platelet concentrate transfusion-associated sepsis, the bacteria most commonly contaminating platelet concentrates are Staphylococcus epidermidis. Sepsis caused by transfusing bacterially contaminated platelet concentrates is seen not uncommonly. Platelets are stored at room temperature and provide an environment for possible bacterial proliferation.

A rare, autosomal recessive qualitative platelet disorder which can cause severe bleeding problems and is associated with large platelets on peripheral blood smear. In light transmission aggregometry testing, there is absent or markedly reduced platelet agglutination with ristocetin.

The Bg(a) antigen belongs to the HLA antigen system. Anti-Bg(a) antibodies are usually formed in response to transfusion or pregnancy, and rarely cause any clinically significant hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN). Crossmatch-compatible RBC units may be provided.

Special fluid that is within vessels of the cardiovascular system and is comprised of cellular components (e.g. red blood cells, white blood cells and platelets) and plasma with proteins (e.g. clotting factors, vW factor, etc.).

The soft spongy cellular area in between the trabecular bony areas inside of the bone where blood's cellular components (e.g. red blood cells, white blood cells, and platelets) are produced.

- Transfer of healthy bone marrow cells to an individual with diseased or damaged bone marrow.

The c antigen belongs to the Rh antigen system. Anti-c antibodies are usually formed in response to transfusion or pregnancy. Anti-c antibodies are clinically significant and can cause acute or delayed hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN) if the patient is challenged with antigen positive blood.

The C antigen belongs to the Rh antigen system and is highly immunogenic. Antibodies to the C antigen are usually formed in response to exposure to antigen-positive blood during transfusion or pregnancy. Anti-C antibodies are clinically significant and may result in acute or delayed hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN) if the patient is challenged with antigen positive blood.

The C(w) antigen belongs to the Rh antigen system. C(w) antibodies are usually formed in response to transfusion or pregnancy and can cause mild hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN).

Also known as intraoperative cell salvage, a method that reuses a patient's own blood after extracorporeally (outside the body) washing and filtering it to avoid or lessen the need to transfuse allogeneic blood (someone else's blood) during surgery.

Antibodies associated with hemolytic disease of the newborn and/or hemolytic transfusion reactions and which are usually reactive at 37 degrees Celsius during serologic testing.

Proteins within blood plasma involved in the formation and stabilization of the blood clot. Common examples include factors I, II, V, VII, VIII, IX, X, and XI. Each clotting, or coagulation, factor must be present in sufficient quantity in order for normal clotting to occur, but the level required is different for each factor.

With regards to blood products, CMV-negative indicates a blood product from a CMV seronegative donor. CMV can be dangerous to individuals with weakened immune systems, newborns and people undergoing organ transplants. For these individuals, having a blood donor who is CMV negative (never been exposed) is important.

Cold-agglutinins:Antibodies that cause agglutination of red blood cells (RBCs) at low temperature, otherwise known as cold agglutinins, are common. Low titers are frequently identified in healthy individuals and are clinically insignificant. Elevated titers (>1:32) are associated with several disease states, such as Mycoplasma pneumoniae infection or lymphoproliferative disorders. Cold agglutinins often have blood group specificity for the I-i system and usually belong to the IgM class of antibodies. As such, they typically cannot cross the placental membrane and are not likely to be a significant risk for hemolytic disease of the fetus and newborn (HDFN). Rarely, the thermal range of cold agglutinins can extend up to body temperature and result in agglutination and lysis of RBCs, such as in Raynaud phenomenon and hemoglobinuria in cold weather (cold agglutinin syndrome). Cold agglutinins have also been reported to cause cardiac ischemia during procedures that use cold cardioplegia. Keeping the patient warm and warming of the blood prior to transfusion may help to prevent agglutination and lysis of RBCs.

Autoantibodies that cause in vitro agglutination of red blood cells during serologic testing performed at temperatures below 37 degrees Celsius and may be seen in children or adults with certain infections or lymphomas.

Group of proteins (~30) that, once activated, are used to help destroy pathogens in the body. Many complement proteins occur in serum as inactive enzyme precursors (zymogens), and others reside on the cell surfaces. Some red blood cell antibodies can activate the complement cascade and cause hemolytic transfusion reactions.

Also known as CBC which includes a count (per volume unit) of the white blood cells, hemoglobin, hematocrit and platelets. When a differential count is added to the CBC, the different types of WBCs are quantitated (e.g. percent neutrophils, lymphocytes, monocytes, eosinophils and basophils).

Umbilical cord blood can be used as a source of stem cells--or hematopoietic progenitor cells--for transplant in those with certain diseases; it is obtained during a delivery only after consent by the mother.

Used for those who are truly platelet refractory and cannot get an adequate increase in their platelet count after transfusion due to an immune-mediated process (proven with multiple 1h post-transfusion platelet counts). Selection of crossmatched platelets involves testing the patient's plasma against donor platelets--if non-reactive, those platelets are considered crossmatch compatible.

Plasma in which the cryoprecipitate containing certain coagulation factors is reduced through centrifugation. That cryosupernatant can be used as a low-volume way to replace coagulations factors such as factor VIII, von Willebrand factor, fibrinogen, etc.

Phenomenon of blood proteins (predominantly immunoglobulins) that precipitate out of the blood and adhere together. They can often be identified on a peripheral blood smear and can be associated with numerous disease processes, including, but not limited to, infectious etiologies, such as hepatitis, autoimmune/connective tissue disorders, and hematopoietic disorders.

A blood product that is stored frozen but thawed prior to its transfusion as a source of certain coagulations factors, such as factor VIII as well as factor XIII, von Willebrand Factor (VWF) and fibrinogen.

Following centrifugation of plasma, cryosupernatant is the portion containing coagulation factors. It contains von Willebrand's factor, factors XIII, and fibronectin. However, it is low in factor VIII and fibrinogen (unlike cryoprecipitate).

Cytokines are a large, diverse family of small proteins or glycoproteins that can influence both innate and adaptive immune responses by acting as molecular messengers between cells.

CMV is a Herpesvirus that can be problematic in immunocompromised individuals and the risk of it being acquired through a transfusion is mitigated through leukocyte-reduced blood and/or by providing CMV-seronegative blood (provided the recipient has not already been exposed).

The D antigen is part of the Rh antigen system, and antibodies against it can cause hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN). Anti-D antibodies usually develop after transfusion of D-positive RBCs or during pregnancy with a D-positive conceptus.

A transfusion reaction causing hemolysis at least 24 hours after a transfusion. It can be asymptomatic or mimic other conditions and may be misdiagnosed. Anti-JKa and anti-JKb are the most commonly encountered antibodies responsible for DHTR. It can rarely be accompanied by intravascular hemolysis.

See "Disseminated intravascular coagulation."

The Diego system (DI) is a blood group antigen system which can be associated with hemolytic disease of the fetus and newborn as well as hemolytic transfusion reactions.

Also known as DAT, it is a test performed to detect antibodies present on the patient's red blood cells (in vivo), and is often performed if there is suspicion of a transfusion reaction. The DAT is also utilized to aid in the diagnosis of hemolytic disease of the newborn and autoimmune hemolytic anemia to investigate possible RBC sensitization by drugs.

Also known as DIC. Process that can ultimately lead to multiorgan dysfunction, DIC is a robust activation of coagulation, fibrin formation and fibrinolysis, microthrombi formation, and platelet comsumption. In the context of transfusion medicine, consider this possibility in patients exhibiting a poor response to platelet transfusions, especially when the 1 hour post-transfusion platelet count is consistent with a non-immune etiology.

Criteria to aid in identifying individuals who are physiologically healthy enough and likely free of infectious diseases prior to donating blood products. May appear on standardized examinations so it is a good idea to be familiar with them.

Also known as DIIHA. Immune-mediated destruction of blood cells and/or platelets by drug-induced antibodies. Depending on the medication, the drug may or may not still be present in the patient for this to occur.

A blood group antigen system designated by the symbol Fy which are predominantly IgG antibodies and clinically significant, associated with hemolytic disease of the fetus and newborn (HDFN) as well as acute and delayed hemolytic transfusion reactions (HTRs).

The e antigen belongs to the Rh antigen system. Anti-e antibodies are usually formed after transfusion of RBCs or during pregnancy. Anti-e antibodies are clinically significant and can cause hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN).

The E antigen belongs to the Rh antigen system. Anti-E antibodies are usually formed in response to transfusion or pregnancy. Anti-E antibodies are clinically significant and can cause acute or delayed hemolytic transfusion reactions, if the patient is challenged with antigen positive blood, or hemolytic disease of the fetus and newborn (HDFN).

A member of the Rh antigen system, E/e are part of a closely linked set of alleles, which includes D/d and C/c, and are typically inherited as a set. As part of the Rh system, E/e antigens are associated with hemolytic disease of the fetus and newborn (HDFN) and hemolytic transfusion reactions (HTRs).

Computer-verified rather than serologic crossmatch to ensure compatibility between the potential recipient of a blood transfusion with the donor blood product. The software interprets the data using a set of precisely defined rules, and if the rule-based criteria for compatibility are not met, or if essential data are missing, a warning message is generated.

The release of blood product(s) which have not undergone a full type and crossmatch; a physician requesting emergency transfusion has assumed the risk of forgoing pretransfusion work-up in an effort to provide blood products for transfusion immediately for a life-threatening situation.

Removal of a component of a patient's blood with subsequent repletion of that same component from donated blood products. An examples of an exchange transfusion includes red cell exchange in patients with sickle cell disease, whereby blood which contains a high percentage of sickled cells are removed and packed red blood cell units without sickled cells are transfused.

While Factor VII is part of the extrinsic pathway of the coagulation cascade, recombinant Factor VII is a product approved for those with congenital factor VII deficiency. Off-label uses include massive transfusion settings.

Transfusion reaction in which fever is identified during or shortly after transfusion of a blood product but there is no clinical or laboratory evidence of hemolysis. The differential diagnosis of fever associated with transfusion includes, but is not limited to, acute red cell hemolysis, sepsis from a contaminated product, or transfusion-related acute lung injury (TRALI).

Also known as FMH. Occurs when fetal blood enters the maternal circulation from any number of causes, which can lead to development of maternal antibodies directed at red blood cells of the fetus and potentially result in hemolytic disease of the fetus and newborn.

In the blood bank, flow cytometry can be used as a complementary or replacement test for red cell immunology, including RBC-bound immunoglobulins and red cell antigens.Flow cytometry has been used to accurately identify and phenotype the recipient’s red cells. Flow cytometry is being used increasingly in the blood bank to assess leukocyte contamination in leukocyte-reduced blood products.

Also known as febrile non-hemolytic transfusion reaction. A type of transfusion reaction in which fever is identified during or shortly after transfusion of a blood product but there is no clinical or laboratory evidence of hemolysis. The differential diagnosis of fever associated with transfusion includes, but is not limited to, acute red cell hemolysis, sepsis from a contaminated product, or transfusion-related acute lung injury (TRALI).

Also known as FFP. Used primarily for repletion of coagulation factors. Fresh frozen plasma specifically must have been frozen within 8 hours of collection via either apheresis donation or after processing whole blood.

The Fy(a) antigen belongs to the Duffy antigen system. This antigen is a glycoprotein that is expressed on the red cells, as well as other tissues, including brain, kidney, spleen, heart, and lung. Anti-Fy(a) antibodies are common and are usually formed in response to transfusion or pregnancy. Anti-Fy(a) can cause acute or delayed transfusion reactions or hemolytic disease of the fetus and newborn (HDFN).

Graft-versus host disease, transfusion associated (TA-GVHD). A severe, potentially fatal transfusion reaction associated with rash, gastrointestinal symptoms, and elevated liver transaminases secondary to lymphocytes present in donor blood which attack the recipient’s organs. Irradiation of blood products prior to transfusion when clinically indicated can help prevent this.

Used for those with severe neutropenia, granulocyte transfusions are collected from directed donors or from pooled apheresis donations and must be ABO compatible with the recipient--not because of the granulocytes themselves but because of the amount of incidentally transfused red cells present in the product.

The antigen that serves as the precursor for the A and B antigens—which convey a person’s blood type. If the H antigen is not further converted to one of those antigens, the blood type is O and those red blood cells possess a large amount of H antigen on their surfaces. Those with A or B blood types have varying amount of remaining H antigen present on the surface.

Stands for Hemolysis, Elevated Liver enzymes, and Low Platelets. A complication of preeclampsia which results in a thrombotic microangiopathic anemia which, if untreated, can be fatal to the mother and fetus. This condition is primarily treated with delivery.

Also known as Hct. Defined as a percentage of blood that is taken up by red blood cells. A low level is usually indicative of anemia. The normal ratio of hemoglobin to hematocrit is about 1:3 (e.g. Hemoglobin of 10 g/dL usually correlates with a Hematocrit of 30%).

A major protein in red blood cells (RBCs) that is responsible for carrying oxygen. It is composed of four peptide chains. The three major normal hemoglobins are Hb-A (2 alpha chains and 2 beta chains), Hb-A2 (2 alpha chains and 2 delta chains), and Hb-F (2 alpha chains and 2 gamma chains). Hemoglobin can be measured along with the Hematocrit, WBC and platelets as part of a routine CBC (complete blood count). Decreased hemoglobin and Hct levels are indicative of anemia.

Genetic diseases that are associated with abnormal hemoglobins due to a mutation that usually leads to a structural abnormality in the hemoglobin molecule. Examples include sickle cell disease (HbSS), HbSC, HbE, and HbCC disease. In contrast to hemoglobinopathies, the defect in thalassemias leads to underproduction of the globin chains rather than a structural abnormality.

Also known as HDFN. Produces an alloimmune reaction of maternal IgG molecules (directed against fetal RBC antigens) that cross the placenta and induce hemolysis and destruction of the fetal RBCs.

Also known as HTR. Antibodies formed by the recipient of a transfusion which attack and destroy cells of the donor present in the blood component.

A group of hereditary genetic coagulation disorders that includes hemophilia A, Hemophilia B, and Hemophilia C. Hemophilia A and B are X-linked disorders while Hemophilia C is an autosomal disorder. Hemophilia A is the most common form of the disorder and is characterized by Factor VIII deficiency. Hemophilia B is less common and is characterized by Factor IX deficiency. Hemophilia C is a lack of Factor XI. Symptoms may vary in severity but usually consist of internal and/or external bleeding (e.g. large joint bleeds).

Adequate control of bleeding.

High titer, low avidity antibodies are usually alloantibodies to antigens which are present in low numbers on red blood cells and are thus weakly reactive. These antigens include: residual HLA antigens, Chido and Rodgers (located on the complement protein C4), and the Knops blood system which includes York (Yka), Knops (Kna and Knb), and McCoy (McCa and McCb) (located on complement receptor type 1). The majority of the red cell antigens to which HTLAs are formed are present at high frequency in the population. These antibodies usually do not cause increased red cell destruction when incompatible blood is transfused or hemolytic disease of the fetus and newborn, although rare case reports of acute hemolytic transfusion reactions are present in the literature (Hoppe et al., Vox Sanguinis (2002), 82: 207-210).

Also known as human immunodeficiency virus. A virus which causes Acquired Immunodeficiency Syndrome (AIDS). Relevant to transfusion medicine because patients should be counseled on risk of transmission (approximately 1 in 1.5 million) prior to consenting for a blood transfusion. Nucleic acid testing of donated blood during the infectious disease screening process has reduced the "window period," in which a patient can be serologically negative and yet be viremic, to roughly 16 days.

Also known as human leukocyte antigens. Represent a complex of genes located on chromosome 6 whose gene products are involved with immune functions, especially the ability of cells in the body to recognize self and non-self antigens. HLAs are very relevant in the context of proper donor selection for organ transplants and can be an immune-mediated cause of a poor response to platelet transfusions.

These are antibodies to human leukocyte antigens, which are primarily IgG antibodies. In the context of transfusion medicine, these can be a cause of immune-mediated platelet refractoriness—a poor response to a platelet transfusion not caused by non-immune etiologies, such as disseminated intravascular coagulopathy, sepsis, splenic sequestration, or medications, to name a few.

Human Leukocyte Antigens Class I are glycoproteins present primarily on the cell surfaces of platelets and most nucleated red blood cells and which are involved in antigen-presentation to CD8 T-lymphocytes.

Human Leukocyte Antigens Class II are present primarily on lymphocytes, monocytes/macrophages, and endothelial cells and are involved in recognition of self and non-self antigens.

Platelets that are HLA compatible between donor and recipient can be offered to diminish immune-mediated platelet refractoriness—or a poor 1 hour response to a platelet transfusion—when it is due to HLA alloimmunization and not other antibodies.

Also known as human T-cell lymphotropic virus (types I/II). These are retroviruses that cause a T-cell proliferation. HTLV-I has been associated with adult T-cell leukemia and a progressive myelopathy. The virus is screened for during donor infectious disease screening using an enzyme immunoassay. The risk of transmission through blood transfusion is roughly 1 in 3 million.

Also known as HLA. Represent a complex of genes located on chromosome 6 whose gene products are involved with immune functions, especially the ability of cells in the body to recognize self and non-self antigens. HLAs are very relevant in the context of proper donor selection for organ transplants and can be an immune-mediated cause of a poor response to platelet transfusions.

These are polymorphisms in platelet antigens and can stimulate production of alloantibodies in recipients of transfused platelets from donors with different HPAs. These antibodies can cause neonatal alloimmune thrombocytopenia, post-transfusion purpura and some cases of platelet transfusion refractoriness due to infusion of donor platelets.

Mediated by antibody molecules that are secreted by plasma cells. Antibodies protect in three main ways. They can inhibit the toxic effects or infectivity of pathogens by binding to them (neutralization). By coating the pathogens, they can enable accessory cells that recognize the Fc portions of antibodies to ingest and kill the pathogen (opsonization). Antibodies can also trigger activation of the complement system.

Excessive bleeding due to primary causes, such as thrombolytic therapy, or secondary causes, including disseminated intravascular coagulation.

A disorder of reduced serum immunoglobulins caused by any number of etiologies, including primary immunodeficiency syndromes, hematopoietic malignancies, and certain medications. It can also be a cause of a typing discrepancy (i.e., when the forward and reverse ABO types do not match.

I and i antigens have a reciprocal relationship: I is expressed on the red cells of most adults, but not on those of neonates, whereas i is expressed only very weakly on the cells of most adults, but strongly on fetal and neonatal cells.

IgA antibodies, which are found in dimeric form, are found in high concentrations in the mucous membranes, particularly those lining the respiratory passages and gastrointestinal tract, as well as in saliva and tears.

The term is sometimes interchangeably used with antibody, a protein that is produced by B cells (in terminally differentiated B-cells known as plasma cells these immunoglobulins are produced and secreted and are not cell surface bound) which recognize and bind to other proteins or substances (foreign or self antigens). Antibodies can be part of an immune response and help eradicate viruses and bacteria or may be part of an autoimmune destructive processes in hematology such as autoimmune hemolytic anemia or immune mediated platelet destruction (e.g. ITP). The different classes of antibodies are usually based on their heavy chains (e.g. IgA, IgG, IgE, IgD, & IgM).

Also known as IAT. This is previously referred to as the indirect Coombs test and sometimes referred to as an antibody screen. The IAT is an agglutination assay for detecting unbound antibodies present in a person's serum. It can be used to detect IgG antibodies present in sera (which are not directly bound on the person's red blood cells) as well as to "crossmatch" blood prior to a transfusion.

Also known as IVIg. Made from pools of human plasma, IVIg consists of IgG subclasses and is used to treat a variety of autoimmune diseases, immunodeficiencies, and certain viral infections.

Method using gamma rays or x-rays which inactivates lymphocytes present in a donated cellular blood component, thereby preventing transfusion-associated graft versus host disease.

The Jk(a) antigen belongs to the Kidd antigen system. Anti-Jk(a) antibodies are usually formed in response to previous transfusions and may result in acute or delayed hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN). The antibody tends to disappear quickly and is therefore a common cause of delayed hemolytic transfusion reactions.

The Jk(b) antigen belongs to the Kidd antigen system. Anti-Jk(b) antibodies are usually formed in response to previous transfusions and may result in acute or delayed hemolytic transfusion reactions if the patient is challenged with antigen positive blood.,

The Js(a)-antigens belongs to the Kell group. The anti-Js(a) antibodies are acquired after red cell exposure during transfusion or pregnancy. Anti-Js(a) antibodies can cause acute or delayed hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN).

Also known as jumbo FFP. A unit of jumbo FFP is equivalent to 2 units of FFP because it is collected by an apheresis machine. It is used to manage bleeding in patients who require replacement of plasma coagulation factors, to help patients with thrombotic thrombocytopenic purpura (TTP) that need therapeutic plasma exchange, and to serve as a source of plasma for manufacturing purposes.

The K-antigen belongs to the Kell antigen system. It is present on the red cells of 9% of white, 2% of black and rare in East Asian patients. The K-antigen is strongly immunogenic. Anti-K antibodies are usually formed in response to transfusion or pregnancy and can cause both hemolytic transfusion reactions and hemolytic disease of the fetus and newborn (HDFN).

An RBC antigen group that contains immunogenic RBC antigens which may cause transfusion reactions or hemolytic_disease_of_newborn.

The Kidd blood group system (Jk) is defined by two alleles, Jka and Jkb (frequency 0.51 and 0.48 in Europeans). There are three common phenotypes Jk(a+b−), Jk(a−b+) and Jk(a+b+) and a rare null phenotype, Jk(a−b−). Antibodies that target Kidd antigens are a significant cause of delayed hemolytic transfusion reactions. Anti-Kidd antibodies are also a cause of hemolytic disease of the fetus and newborn (HDFN).

Assay which capitalizes on fetal red cells’ ability to resist acid elution while maternal cells cannot, allowing for a rough quantification of fetal maternal hemorrhage.

The Kp(a) antigen belongs to the Kell antigen system. It is present on the red cells of 2.0% of white and <0.1% of black patients. Kp(a) antibody appears to be red cell stimulated, it is often IgG and best reactive by indirect antiglobulin testing (IAT). This antibody has the ability to cause transfusion reactions and hemolytic disease of the fetus and newborn (HDFN).

The Le(a) antigen is part of the Lewis system and is a plasma glycosphingolipid produced by gut epithelium and passively adsorbed onto the red cell membrane. Antibodies to Lewis antigens usually occur without known red cell stimulus and they are predominantly IgM. Transfused donor RBCs shed their own Lewis antigens and assume the phenotype of the recipient within a few days of transfusion (released antigens are then easily neutralized by the anti-Lewis antibodies in the recipient’s plasma). Hemolytic transfusion reactions and hemolytic disease of the fetus or newborn due to Lewis antibodies are rare. It is not considered necessary to find Le(a)-negative donor blood.

Literally means white blood and refers to a neopastic hematopoietic neoplasm of lymphoid or myeloid origin that involves the peripheral blood. They can be immature (Acute) or mature/maturing (Chronic). Acute leukemias include acute myeloid Leukemia (AML) and Acute Lymphoid Leukemia (ALL). Examples of maturing/mature leukemias include chronic myelogenous leukemia (CML) and chronic lymphocytic leukemia (CLL).

Leukocytes reduced whole blood and blood components by using filters have been shown to reduce the following: recurrent febrile, non-hemolytic transfusion reaction, alloimmunization to leukocyte antigens that may complicate care of patients who undergo transplantation or chronic transfusion therapy, and transmission of cytomegalovirus (CMV) to patients at increased risk of CMV disease. Leukocyte reduction is not considered appropriate for the prevention of transfusion-associated graft-versus-host disease.

This blood group is not synthesized by the RBCs, but the antigens derived from body secretions are adsorbed, or incorporated, into the RBC membrane. The Lewis antigen system is associated with the secretor system and ABO blood group system. Le(a-b+)is the most common Lewis phenotype seen in the white population (75%) and the black population (55%). Le(a+b-) occurs in roughly equal proportions in both populations (23%), while Le (a-b-) is far more common in the black population (22%). Lewis antibodies are rarely of clinical significance.

The Lu(a) antigen is part of the Lutheran system. Anti-Lutheran antibodies are rare and are most often produced in response to antigens encountered during pregnancy or prior transfusion. Anti-Lu(a) is rarely associated with hemolytic disease of the fetus and newborn or hemolytic transfusion reactions, and RBCs for transfusion are cross-matched but not typed for Lu(a).

The M antigen belongs to the MNS antigen system. Anti-M antibodies are usually found in the sera of persons who have had no exposure to human red cells. Although M antibodies are generally thought to be predominantly IgM, many examples that are partly or wholly IgG are frequently found. The antibodies are rarely clinically significant. However, in a few exceptional cases, anti-M detectable at the antiglobulin phase has caused hemolytic disease of the fetus and newborn (HDFN) or hemolysis of transfused cells.

The cell-mediated adaptive immune response is regulated by the major histocompatibility complex (MHC). A major role of the MHC is to bind small peptides and to present them to the cell surface where the antigen can be recognized by T cell receptors. MHC molecules display both ‘self’ peptides derived from their own proteins, and foreign peptides derived from invading pathogens. The immune system is constantly monitoring the surfaces of cells, and the MHC-presented peptides help immune cells to discriminate between normal antigens on the surface of all cells, and those that are foreign and potentially dangerous. Defects in certain MHC genes lead to autoimmune disorders in which the body fails to recognize self-antigens, such as occurs in diseases like multiple sclerosis, inflammatory bowel disease, and in some forms of arthritis and diabetes. There are two major classes of MHC molecules. MHC class I molecules (MHC I) consist of one membrane-spanning a chain (heavy chain) produced by MHC genes, and one b chain (light chain or b2-microglobulin) produced by the b2-microglobulin gene. They are present on most cells and bind CD8 adhesion molecules on cytotoxic T cells. MHC class II molecules (MHC II) consist of two membrane-spanning chains, a and b, of similar size and both produced by MHC genes. They are present on antigen-presenting cells and bind CD4 adhesion molecules on helper T cells.

Typically defined as the replacement by transfusion of 10 units of red cells in 24 hours, usually due to trauma or uncontrolled hemorrhage.

The MNS blood group system is second only to the Rh blood group system in its complexity. Many alloantibodies to antigens in the MNS system are not generally clinically significant--these are often “naturally occurring” and if they do not react at 37°C can be ignored in transfusion practice. However, rare examples of anti-M, anti-N, anti-S, -s, and antiU have been reported to cause immediate and delayed hemolytic transfusion reactions and hemolytic disease of the fetus and newborn (HDFN). Anti-M is often cold-reacting IgG and is enhanced by testing in an acidified environment.

Also known as plasma cell myeloma. A plasma cell neoplasm that is usually characterized by increased numbers (10% or more) of monoclonal plasma cells in the bone marrow. Two main types: Asymptomatic (Smoldering) and Symptomatic (characterized by one or more of the following CRAB findings: Remember "CRAB", C for hyperCalcemia, R for Renal disease associated with multiple myeloma, A for anemia associated with the multiple myeloma, and B for lytic Bone lesions).

Also known as NAIT. Caused by transplacental passage of maternal platelet-specific alloantibody and rarely human leukocyte antigen (HLA) allo-antibodies to fetuses whose platelets express the corresponding antigens. The antibodies are specific for platelet antigens inherited from the father but which are absent in the mother. Frequently, the thrombocytopenia is mild and the affected neonates remain largely asymptomatic. In cases of severe thrombocytopenia, the neonates may exhibit hemorrhagic complication at or a few hours after delivery. The most serious complication is intracranial hemorrhage.

A low neutrophil count within the peripheral blood.

Non-specific antibodies lack antigenic specificity and may represent anti-HLA, anti-complement, and other antibodies not identified on the standard antibody panel. The vast majority of non-specific antibodies are clinically insignificant and are not known to cause hemolytic disease of the fetus and newborn.

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This a rare autoimmune hemolytic anemia that is due to cold reacting IgG antibodies to the RBC P antigen. These antibodies bind RBCs at cold temperature and with elevated temperature the bound red cells undergo a complement induced destruction (hemolysis). These biphasic unusual cold reacting IgGs are also known as Donath-Landsteiner antibodies. These patients may undergo hemolysis when exposed to cold temperature and present with hemoglobinuria. Peripheral blood may show some neutrophils with erythrophagocytosis.

Also know as PNH is an acquired complement-induced hemolytic anemia that is due to a mutation of phosphatidylinositol glycan A (PIGA) gene (on chromosone X) which is resposible for making the cell membrane protein anchoring molecule glycosylphosphatidylinositol (GPI). Notably the gene is on chromosome X but unlike X-linked germline mutations (e.g. hemophilia A) which almost exclusively involve males, this acquired mutation involves males and females equally. The diagnosis is made by flow cytometry and showing loss of CD55 (Complement decay accelerating factor) and CD59 (protectin which usually inhibits the complement membrane attack complex) on multiple blood cell types (RBCs and WBCs). These patients are also at an increased risk of thrombosis.

Only part of the D antigen is present on the red cell surface, so antibodies may be formed to the missing part. Partial D individuals, once identified as such, should receive Rh-negative blood and may require RhIg in certain clinical circumstances.

DNA virus that causes a childhood febrile illness in children and red cell aplasia in adults and can potentially be transmitted through a blood transfusion, specificially with factor concentrates, although the risk of it causing disease is rare.

Potential complication following stem cell or organ transplant whereby lymphocytes from the donor proliferate and make antibody against the recipient, leading to an immune-mediated hemolysis.

Process which involves centrifuging and separating blood into various components, via a machine, removing the plasma component, and returning the rest back into circulation. It can be done for therapeutic purposes or as a means of donor collection.

Repeated failure to show an adequate increase in platelet count after platelet transfusions. In general, platelet refractoriness can be immune or non-immune mediated. Immune causes of platelet refractoriness include ITP, antibodies to HLA, platelet-specific antibodies, or drug induced antibodies. Non-immune causes of platelet refractoriness include fever, infection, splenomegaly, DIC, TTP, or hematopoietic progenitor cell transplantation.

Cellular fragments (2-3 um in diameter which correlates to about 1/3 to 1/2 the size of a RBC) released from megakaryocytes into the blood and involved in hemostasis.

Relatively rare complication following transfusion (typically at least one day or up to several weeks later) that manifests as thrombocytopenia and purpuric rash, often secondary to human platelet antigens.

The D antigen is part of the Rh antigen system, and antibodies against it can cause hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN). Anti-D antibodies usually develop after transfusion of D-positive RBCs, during pregnancy with a D-positive conceptus, or are detected following recent administration of anti-D antibodies (RhoGAM). The anti-D antibodies present in this patient’s plasma likely represent passive immunization by RhoGAM.

Abbreviated as PT, it is often used along with a partial thromboplastin time (PTT) to help determine the cause of unexplained bleeding or inappropriate blood clotting. The PT evaluates the coagulation factors VII, X, V, II and I (fibrinogen).

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Collected by apheresis instruments which selectively removes platelets; one unit is one dose for an adult. Should be >3.0 x 10^11 in 90% single units tested per AABB standards.

Also called RBC or erythrocyte, are the most common type of blood cell in the body. It's role is to deliver oxygen via the hemoglobin molecule to various tissues and organs.

The Rh blood group system is the most polymorphic of the human blood groups, consisting of at least 45 independent antigens and, next to ABO, is the most clinically significant in transfusion medicine. Alloantibodies that recognize Rh antigens are usually IgG and react by the indirect antiglobulin test. Alloantibodies in the Rh blood group system can cause destruction of transfused RBCs and of fetal RBCs in hemolytic disease of the fetus and newborn (HDFN).

The s antigen belongs to the MNS antigen system. Anti-s is usually formed after red cell immunization via transfusion or pregnancy, and may result in hemolytic disease of the fetus and newborn (HDFN) or hemolytic transfusion reactions if the patient is challenged with antigen positive blood.

In the context of transfusion medicine, series of assays used to determine blood and Rh type, identifiy the presence and identity of any antibodies present in a person's serum/plasma, and determine whether or not a transfusion reaction was due to an immune-mediated process.

Transfusion therapy is a key intervention in decreasing morbidity and mortality in patients with sickle cell disease. Despite the recognized benefits of transfusion therapy, it is not without the risks of iron overload, alloimmunization, and delayed hemolytic transfusion reactions.

Collected by apheresis instruments which selectively removes platelets; one unit is one dose for an adult. Should be >3.0 x 10^11 in 90% single units tested per AABB standards. Can collect HLA-matched or crossmatched platelets from a single donor based on testing.

A family of inherited blood disorders that is characterized by decreased production of either alpha or beta-globin chains of the hemoglobin molecule. The two major types of thalassemias are alpha_thalassemia (decreased alpha chain production) and beta_thalassemia (decreased beta chain production). The decreased hemoglobin production results in microcytic (low MCV; <80) red blood cells. Underproduction of one globin chain typically results in stimulating the bone marrow to increase its production of RBCs (as opposed to iron deficiency anemia where there is typically a decrease in RBCs). Hence, in cases of thalassemia the ratio of MCV/RBC is typically lower (<13) than that seen in iron deficiency anemia (usually a ratio of >15). Note: As opposed to hemoglobinopathy which produces abnormal hemoglobin molecules, the hemoglobin molecules produced in thalassemias are decreased but normal in function.

Plasma that has been removed from the freezer and brought to a stored temperature of 1 to 6 degrees Celsius and which can be transfused within 5 days, albeit with slightly lower levels of coagulation factors V, VII, and VIII.

A low platelet count within the peripheral blood.

Also known as TEG, it is a hemostatic assay that measures the global viscoelastic properties of whole blood clot formation under low shear stress. It demonstrates the interaction of platelets with the coagulation cascade (aggregation, clot strengthening, fibrin cross linking and fibrinolysis).

A protein (hormone) produced by the liver and kidney that stimulates production and differentiation of megakaryocytes and ultimately stimulates the production of more platelets. Note: "Thrombo" refers to platelets and "-poietin" refers to its ability to stimulate production.

(TTP) A microangiopathic hemolytic anemia (MAHA) that is usually due to a deficiency of ADAMTS-13 (a metalloprotease responsible for cleavage of large multimers of vW factor). Similar to hemolytic uremic syndrome (HUS) remember the mnemonic "Brain FART" (Complements of Dr. M. Baughn) which is Brain for neurologic problems (more commonly associated with TTP than HUS), F for Fever, A for Anemia, R for Renal failure (more commonly associated with HUS than TTP), and T for Thrombocytopenia. On peripheral smear, usually schistocytes are easily notable and increased in number (similar to other MAHA).

Also known as transfusion related acute lung injury. It is a transfusion reaction which includes symptoms of acute dyspnea, hypotensiona and fever occuring during or within six hours of a transfusion, and which causes a pattern of lung injury resembling acute respiratory distress syndrome (ARDS) on x-ray. TRALI is thought be immune-mediated by human leukocyte antigen (HLA) antibodies and/or human neutrophil antigen (HNA) antibodies present in the transfusion.

Adverse events following transfusion of a blood component of which there are several and which vary in severity, from mild to potentially fatal.

Also known as TRALI. It is a transfusion reaction which includes symptoms of acute dyspnea, hypotensiona and fever occuring during or within six hours of a transfusion, and which causes a pattern of lung injury resembling acute respiratory distress syndrome (ARDS) on x-ray. TRALI is thought be immune-mediated by human leukocyte antigen (HLA) antibodies and/or human neutrophil antigen (HNA) antibodies present in the transfusion.

Serologic testing sequence to identify and confirm a patient’s blood type, identify any antibodies present in the patient’s serum, and test units of blood in the inventory that would be compatible for a transfusion. Typically ordered when the likelihood of the patient requiring a transfusion is greater than 50%.

Infrequently ordered, the type and hold confirms the patient’s ABO/Rh-type only.

Serologic testing sequence to identify and confirm a patient’s blood type and identify whether or not there are antibodies in the patient’s serum. Typically ordered when there is less than 50% chance that a blood product transfusion will actually be required.

Retrospective analysis to monitor blood component ordering trends with the overarching goals of decreasing wastage of blood products and optimize patient safety.

The V antigen is a member of the Rh antigen group and is present on nearly 30% of RBCs of black patients but is rare among white patients. The V antigen is the product of Ro and r alleles. Anti-V antibodies can cause both hemolytic disease of fetus and newborn (HDFN) and immediate and delayed hemolytic transfusion reactions.

Fluids that do not contain blood components, such as Lactated Ringer's and saline, which can be transfused for hypovolemic conditions.

A hereditary or acquired coagulation disorder resulting from either a qualitative change of vWF (usually a mutation giving rise to an abnormal vWF) or quantitative deficiency of vWF. There are three types of hereditary vWF deficiencies: Type 1, Type 2, and Type 3. Type 1 is the most common form and is a quantitative defect where vWF are decreased. Most patients are asymptomatic; however, symtoms such as prolonged bleeding post-surgery, menorrhagia, or easy bruising can occur. Type 2 is subdivided into 2A, 2B, 2M, and 2N, and it is a qualitative defect of vWF. Type 2B is unique in that the mutation leads to an increased binding of platelets to vWF and increased clearance thus producing a mild thrombocytopenia. Type 2M and 2N are rare. Type 3 is the most severe form and has no detectable levels of vWF.

Warm autoantibodies (WAA) may occur at any age, and are more common in persons with autoimmune disease, B-cell malignancies (such as CLL), HIV infection, or with exposure to certain drugs such as cephalosporins and Septra. A minority of persons with positive WAA develops autoimmune hemolytic anemia, in which case the patient should be evaluated for signs of hemolysis (e.g., LDH, bilirubin, haptoglobin, and hematocrit determinations).

Saline rinse of cellular blood products, such as platelets and packed red blood cells, to remove residual plasma. The process delays how quickly a blood product can be made available for transfusion, is costly, and can diminish the overall quality/functionality of the component, but may be necessary in select clinical scenarios.

A qualitative defect in D antigen expression, potentially resulting in a D- positive individual typing as D-negative. Weak D testing is performed on blood donors to ensure true Rh-positive blood (D-positive) is not inadvertently transfused to an Rh-negative (D-negative) individual.

RNA virus that can cause meningitis, encephalitis, and flu-like symptoms and has rarely been acquired through blood transfusions. It is screened for using nucleic acid testing on pooled donor units. In highly endemic areas, reference labs may screen individual units.

Whole blood is no longer commonly available or used in most of the United States. Whole blood, if available, may be indicated for large volume hemorrhaging, such as seen with major trauma, requiring massive transfusion and rapid correction of anemia, coagulopathy, acidosis, and hypothermia.

The Wright blood system is a pair of antigens, Wr(a) and Wr(b), carried on the Band 3 glycoprotein AE1 inherited through various alleles of the gene SLC4A1. Wr(a) is a low-frequency antigen found on the RBCs of approximately 1: 1000 Caucasians. Anti-Wr(a) can be naturally occurring or can be the result of red cell alloimmunization. It has been reported to be present in 1:25 to 1:100 healthy blood donors and even higher proportion of hospital patients. Incompatibility due to anti-Wr(a) can cause acute or delayed hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN) if the patient is challenged with antigen positive blood.

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Gastrointestinal disease-causing bacteria that has been implicated in some transfusion reactions, specifically packed red blood cell transfusions, since the organism can survive at the colder storage temperatures that red cells require.

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