PA H12 | Blood Groups & Transfusion Medicine — Glossary

An IgM-mediated, complement-activated intravascular haemolysis of donor red cells occurring within 24 hours of transfusion, most commonly due to ABO incompatibility from clerical error.

Withdrawal of 1–3 units of the patient's blood at induction of anaesthesia with simultaneous crystalloid/colloid replacement; units stored at room temperature and re-infused at surgery's end.

The visible clumping of RBCs caused by antibody cross-linking antigens on adjacent cells; the basis of direct blood group typing in the ABO system.

An immune reaction directed against antigens from another individual of the same species — as distinct from autoimmune (self) or xenoimmune (cross-species) responses.

Development of antibodies against foreign (non-self) red cell antigens after exposure through transfusion or pregnancy; complicates future crossmatching and transfusion in sensitised patients.

A secondary (boosted) immune response occurring on re-exposure to an antigen; in DHTR, re-exposure to a red cell alloantigen rapidly elevates IgG antibody levels that were previously below detectable thresholds.

Passively administered anti-D IgG given to Rh-negative pregnant women to prevent sensitisation; it rapidly clears fetal Rh+ RBCs from the maternal circulation before the maternal immune system can mount a primary response.

Antibody raised against human immunoglobulin (IgG) and complement; bridges cell-bound IgG antibodies causing agglutination, enabling detection of warm-reactive alloantibodies in the AHG phase of crossmatch.

Antibodies directed against HLA antigens on donor leukocytes; formed through prior transfusion or pregnancy; responsible for FNHTR and TRALI.

Continuous-flow blood separation technique that selectively collects one component (platelets, plasma, or granulocytes) from a donor while returning the remainder.

Collection and re-infusion of a patient's own blood, eliminating risks of alloimmunisation and transfusion-transmitted infections associated with allogeneic blood.

Introduction of bacteria into a blood component during collection, processing, or storage; the commonest infectious cause of transfusion-related death, particularly from platelet components stored at room temperature.

A mandatory two-identifier verification performed at the patient's bedside before each unit is administered, confirming the patient's identity (wristband name + date of birth/hospital number) against the unit label and compatibility report.

A genetically determined molecule (oligosaccharide or protein) on the RBC surface that can elicit an alloimmune response in an individual who lacks it.

A rare blood group in which the H gene is non-functional, producing no H substance and therefore no ABO antigens; plasma contains anti-A, anti-B, and anti-H; only Bombay-type donors are compatible.

IgG-sensitised red cells added to every negative AHG test result; they must agglutinate to confirm the AHG reagent was active — failure to agglutinate invalidates the test.

Hypocalcaemia caused by citrate anticoagulant (from blood bags) chelating free ionised calcium; significant during massive transfusion or in patients with liver failure who cannot metabolise citrate.

A herpesvirus transmitted via leukocytes in blood; harmless in immunocompetent recipients but causes severe opportunistic disease (pneumonitis, retinitis) in immunocompromised patients and neonates.

High-titre IgM autoantibodies that react at temperatures below 30°C; can cause spontaneous RBC agglutination at room temperature during blood-grouping, managed by performing all testing at 37°C.

Transfusion practice in which separated blood fractions (PRBC, platelets, plasma) are given individually to address specific deficits, replacing whole-blood transfusion.

Cold-insoluble precipitate from thawed FFP, rich in fibrinogen, Factor VIII, vWF, and Factor XIII; the preferred component for isolated fibrinogen replacement.

The most immunogenic of the Rh blood group antigens, encoded by the RHD gene; its presence or absence defines Rh-positive and Rh-negative status respectively.

Extravascular haemolysis occurring 2–14 days post-transfusion due to an anamnestic IgG antibody response to a red cell alloantigen (commonly Rh or Kidd system).

Acquired coagulation deficiency resulting from replacement of blood volume with components (e.g., PRBC) that lack clotting factors and platelets; prevented by 1:1:1 transfusion ratio.

A laboratory test that detects immunoglobulin or complement proteins bound to the surface of red blood cells; positive in immune haemolytic anaemias and AHTR.

A small ancillary bag in the blood collection set that diverts the first 10–20 mL of collected blood (highest bacterial load from skin plug) away from the main collection bag, reducing bacterial contamination rates.

Temporary or permanent exclusion of a potential blood donor based on risk factors for TTI (e.g., febrile illness, high-risk behaviour, travel history); the first layer of the multi-layer blood safety strategy.

A blood group system whose antigens (Fy(a), Fy(b)) serve as the receptor for Plasmodium vivax; Duffy-null individuals (common in West Africans) are resistant to P. vivax malaria.

Computer-based ABO/Rh compatibility confirmation without serological cell mixing; valid only when two concordant ABO typings exist, the antibody screen is negative, and the laboratory system is validated.

The presence of large numbers of immature nucleated RBCs (erythroblasts) in fetal circulation, reflecting increased haematopoiesis in response to severe haemolytic anaemia in HDN.

Destruction of antibody-coated RBCs by macrophages (Fc receptor-mediated phagocytosis) in the spleen and liver; the mechanism in Rh-mediated HDN and delayed transfusion reactions.

The most common transfusion reaction; fever and chills caused by cytokines from donor leukocytes or recipient anti-HLA antibodies, without haemolysis or haemodynamic compromise.

The passage of fetal RBCs into the maternal circulation, most commonly at delivery; the sensitising event in Rh HDN in Rh-negative mothers carrying Rh-positive fetuses.

Testing patient red blood cells against known commercial antisera (anti-A, anti-B, anti-D) to identify surface antigens and assign ABO/Rh blood group.

Plasma frozen within 6–8 hours of collection to preserve labile coagulation factors (V and VIII); thawed at 37°C; used for multiple factor deficiencies, DIC, and TTP plasma exchange.

Exposure of cellular blood products to ionising radiation to inactivate donor T-lymphocytes; mandatory for immunocompromised recipients to prevent TA-GVHD.

A blood-grouping technique using micro-columns of dextran-acrylamide gel; agglutinated cells are trapped in the column while free cells pellet at the bottom, providing a graded, permanent visual result.

An enzyme that adds specific sugar residues to an oligosaccharide chain; A-transferase adds GalNAc (producing A antigen), B-transferase adds galactose (producing B antigen).

Apheresis-collected neutrophil concentrate with 24-hour shelf-life; used for life-threatening infections in severely neutropenic patients unresponsive to antibiotics.

A situation in which forward and reverse ABO grouping results are inconsistent with Landsteiner's rule; transfusion must halt until the cause is identified and resolved.

The oligosaccharide precursor on RBCs formed by the addition of fucose by the H-gene product; the substrate on which A and B transferases act to produce A and B antigens respectively.

Free haemoglobin in the urine from intravascular haemolysis; appears as port-wine or cola-coloured urine; urine dipstick is haem-positive but microscopy shows no red blood cells (distinguishing it from haematuria).

A condition in which maternal IgG alloantibodies (most commonly anti-D) cross the placenta and destroy fetal RBCs, causing fetal anaemia, erythroblastosis fetalis, and potentially hydrops fetalis.

Pathological accumulation of iron in parenchymal organs (liver, heart, endocrine glands) resulting from repeated blood transfusions; each unit delivers ~200 mg of elemental iron that the body cannot excrete.

A systematic surveillance programme for monitoring, reporting, investigating, and analysing adverse transfusion events including TTIs, to improve blood safety and clinical practice.

Hepatitis B surface antigen — the principal serological marker of active or chronic HBV infection, used as the standard blood bank screening test for hepatitis B.

Development of antibodies against donor HLA antigens on leukocytes following repeated transfusion, causing platelet refractoriness; prevented by leukoreduction or HLA-matched platelets.

Human T-lymphotropic virus (types I and II) — a retrovirus transmitted via leukocytes that causes adult T-cell leukaemia/lymphoma (HTLV-I) or tropical spastic paraparesis; not currently in India's mandatory screening panel.

A severe, life-threatening condition characterised by generalised oedema, ascites, and pleural effusions in the fetus, resulting from high-output cardiac failure due to severe fetal anaemia in HDN.

The commonest primary immunodeficiency (~1 in 500); affected individuals may form anti-IgA antibodies; transfusion with IgA-containing blood products can trigger severe anaphylaxis.

First phase of serological crossmatch performed at room temperature after brief centrifugation; rapidly detects ABO incompatibility and IgM alloantibodies within minutes.

An alloantibody formed only after antigenic stimulation (transfusion or pregnancy); typically IgG; contrasted with naturally occurring (IgM) antibodies of the ABO system.

Laboratory test that detects IgG antibodies in serum that have bound to red cell antigens; used in the AHG phase of crossmatching and antibody screening.

Aspiration, anticoagulation, washing, and re-infusion of blood shed in the operative field using a cell-saver machine; contraindicated when the field is contaminated by bowel contents or infection.

Destruction of RBCs within the blood vessels, releasing haemoglobin directly into the plasma; caused by complement-mediated MAC formation, as in ABO-incompatible transfusion.

Treatment of blood components with gamma rays or X-rays (25–50 Gy) to inactivate donor T-lymphocytes and prevent transfusion-associated graft-versus-host disease (TA-GvHD).

A highly immunogenic blood group system; anti-K causes severe HDN partly by suppressing fetal erythropoiesis in addition to causing haemolysis.

A blood group system whose antibodies (anti-Jk(a)) are notorious for causing delayed haemolytic transfusion reactions because their titre falls below detectable levels between exposures.

The principle that the plasma always contains IgM antibodies directed against the ABO antigens absent from one's own red blood cells.

An individual's serum contains the ABO antibody (isohaemag-glutinin) against the ABO antigen they lack on their red cells; forward and reverse grouping results must conform to this rule.

Removal of leukocytes from blood products by filtration; reduces but does not eliminate FNHTR, and does not prevent TA-GVHD.

Removal of donor leukocytes from blood components using high-efficiency filters to reduce FNHTR, HLA alloimmunisation, and CMV transmission risk.

A blood bank protocol that traces all recipients of blood components from a donor subsequently found to be infected with a TTI, to offer testing, counselling, and treatment.

Pre-transfusion compatibility test mixing donor red blood cells with recipient serum; detects recipient antibodies reactive with donor antigens — the critical safety test before transfusion.

Transfusion of ≥10 units of PRBC within 24 hours (or replacement of one full blood volume); associated with metabolic complications including citrate toxicity, hyperkalaemia, and dilutional coagulopathy.

The terminal complex of the complement cascade (C5b-9) that inserts into and lyses the lipid bilayer; responsible for intravascular haemolysis in ABO-incompatible transfusion.

Pre-transfusion test mixing donor serum with recipient red cells; detects donor antibodies against recipient antigens; less critical with packed red cells containing minimal plasma.

A naturally occurring alloantibody (IgM) against ABO antigens absent from one's own RBCs; present from infancy due to environmental cross-reactive antigen stimulation, without the need for prior transfusion.

A molecular technique (PCR or transcription-mediated amplification) that detects viral RNA or DNA directly, enabling earlier detection than antibody- or antigen-based tests and thus shortening the window period.

Red cell concentrate prepared by removing most plasma from whole blood; haematocrit 65–80%; stored at 2–6°C for up to 42 days.

A method (e.g., psoralen + UV-A light, riboflavin + UV) that inactivates a broad spectrum of bacteria, viruses, and parasites directly within a blood component before transfusion; currently available for platelets and plasma.

Therapeutic procedure in which the patient's plasma is removed and replaced with FFP or albumin; used in TTP to remove anti-ADAMTS-13 antibodies and replenish the enzyme.

Suspension of platelets in a small volume of plasma, used for thrombocytopenia or platelet dysfunction; stored at 20–24°C with constant agitation for up to 5 days.

Failure to achieve the expected post-transfusion platelet count increment, due to immune causes (anti-HLA/HPA antibodies) or non-immune causes (fever, sepsis, DIC, splenomegaly).

Severe thrombocytopenia occurring 7–10 days after transfusion, caused by alloantibodies (commonly anti-HPA-1a) that destroy both donor and recipient platelets.

Collection of the patient's own blood in the weeks before elective surgery for storage and potential re-transfusion; requires Hb ≥11 g/dL and adequate cardiovascular reserve.

The irreducible probability of a TTI being transmitted even after all standard screening and safety measures have been applied; expressed per unit transfused.

Testing patient serum against known reagent red cells (A cells, B cells) to detect naturally occurring ABO isohaemagglu-tinins; serves as a cross-check on forward grouping.

Stacking of red cells in coin-like rolls due to elevated plasma proteins (fibrinogen, immunoglobulins); a form of pseudo-agglutination that disperses on saline replacement, distinguishing it from true agglutination.

Additive solution (saline, adenine, glucose, mannitol) added to PRBC to extend shelf-life to 42 days by maintaining red cell ATP and preventing haemolysis.

Rare but nearly universally fatal complication in which transfused donor T-lymphocytes engraft in an immunocompromised recipient and attack host tissues; prevented by irradiation of components.

Acute pulmonary oedema secondary to excessive transfusion volume or rate, especially in patients with limited cardiac reserve.

Treponema pallidum haemagglutination assay — a specific treponemal antibody test used as a confirmatory test for syphilis; more specific than VDRL.

Acute non-cardiogenic pulmonary oedema within 6 hours of transfusion, caused by donor anti-HLA or anti-neutrophil antibodies activating recipient neutrophils in pulmonary capillaries.

A life-threatening condition in which viable donor T-lymphocytes engraft in an immunocompromised recipient and attack host tissues; prevented by gamma-irradiation of blood products.

Immune system modulation in the recipient caused by allogeneic white cells and other immunoactive components in donor blood; associated with increased post-operative infections and possibly tumour recurrence.

Any infection acquired by a blood recipient through administration of blood or a blood component, classified as iatrogenic and preventable through blood safety systems.

Microangiopathic haemolytic anaemia caused by deficiency of ADAMTS-13 (vWF-cleaving protease), leading to platelet-rich thrombi in small vessels; treated with plasma exchange using FFP.

A prion disease in humans linked to bovine spongiform encephalopathy; prions are not inactivated by standard sterilisation, making donor deferral (lifetime exclusion for extended UK residence 1980–1996) the only mitigation strategy for transfusion.

Venereal Disease Research Laboratory test — a non-treponemal flocculation test used as a screening test for syphilis (Treponema pallidum infection); reactive results require confirmatory TPHA.

A variant of the Rh D antigen expressed at low density; detected by indirect antiglobulin testing; donors with weak D are labelled Rh-positive to prevent alloimmunisation in Rh-negative recipients.

The interval between a donor's infection and the point at which the standard screening test for that infection turns positive; during this period the donor is infectious but tests negative.

A psychrotolerant Gram-negative bacterium capable of growing in refrigerated red cell concentrates; produces endotoxin that causes severe septic shock when the contaminated unit is transfused.