Immunohematology and Blood Transfusion Medicine Review

Essential vocabulary terms, blood group system characteristics, serological definitions, and transfusion medicine concepts derived from practice exam lecture notes.

Dithiothreitol (DTT)

A sulfhydryl reagent that disrupts disulfide bonds and the tertiary structure of proteins, thereby denaturing Kell blood group system antigens on red blood cells.

Chloroquine diphosphate (CDP)

A chemical reagent used in the blood bank to dissociate IgG antibodies from intact red blood cells without destroying red cell surface antigens.

Low ionic strength solution (LISS)

An enhancement medium containing a reduced concentration of sodium chloride ($0.2\%$\,$NaCl$) that lowers the zeta potential around red blood cells, accelerating antigen-antibody uptake.

Complement (in transfusion serology)

A cascade of serum proteins required for red blood cell lysis following an antigen-antibody reaction; detected in vitro using anti-C3b or anti-C3d reagents.

Neutralization

An antibody identification technique in which soluble substance (such as Lewis substance, saliva, or hydatid cyst fluid) is incubated with serum to bind and inhibit specific antibodies.

H Antigen Expression Hierarchy

The relative quantity of unconverted $H$ antigen present on red blood cells across ABO phenotypes, ordered from most to least: $O > A_2 > B > A_2B > A_1 > A_1B$.

Plasma Protein Fraction (PPF)

A plasma product prepared from large pools of human plasma and pasteurized at $60^\circ\text{C}$ for $10\text{ hours}$, resulting in a virtually eliminated risk of transmitting lipid-enveloped viruses such as hepatitis.

$2+$ Agglutination Reaction

A serological grading defined by the presence of many medium-sized agglutinates in a clear supernatant background upon tube resuspension.

$1+$ Agglutination Reaction

A serological grading defined by numerous small and medium agglutinates suspended in a turbid or cloudy background.

Dolichos biflorus

A plant lectin with anti-$A_1$ specificity that selectively agglutinates red cells carrying the $A_1$ antigen by binding the immunodominant sugar N-acetylgalactosamine.

Bombay Phenotype ($O_h$)

A rare phenotype resulting from the homozygous inheritance of the amorphic $hh$ genotype; red cells lack $H$, $A$, and $B$ antigens (negative with Ulex europaeus lectin) and produce potent, naturally occurring anti-A, anti-B, and anti-H.

Acquired B Antigen

A pseudo-antigen phenomenon seen in group A individuals when microbial enzymes deacetylate the $A$ immunodominant sugar (N-acetylgalactosamine) into galactosamine, which cross-reacts with certain anti-B reagents lacking the ES-4 clone.

RHD and RHCE Genes

The two closely linked genes controlling the Rh blood group system; RHD encodes the $D$ antigen, whereas RHCE encodes the $C$, $c$, $E$, and $e$ antigens.

Partial D Antigen

A variant $D$ antigen phenotype resulting from missing or altered epitopes of the $D$ protein mosaic; individuals can produce alloanti-D when exposed to complete $D$ antigen.

Kidd Blood Group Antibodies

Complement-binding IgG antibodies (anti-$Jk^a$, anti-$Jk^b$) enhanced by proteolytic enzymes that exhibit dosage, deteriorate quickly in vitro and in vivo, and are notorious for causing delayed hemolytic transfusion reactions (DHTR).

Duffy Blood Group System

A blood group system comprising codominant alleles $Fy^a$ and $Fy^b$ that encode antigens sensitive to proteolytic enzymes (ficin, papain); the $Fy(a-b-)$ phenotype confers resistance to Plasmodium vivax malaria.

Thrombotic Thrombocytopenic Purpura (TTP)

A microangiopathic condition characterized by thrombocytopenia and intravascular platelet thrombi, in which platelet transfusions are contraindicated because transfused platelets aggravate thrombosis.

Cryoprecipitate

The cold-insoluble fraction of fresh frozen plasma thawed at $1^\circ\text{C}-6^\circ\text{C}$; enriched in Factor VIII ($\ge 80\,\text{IU}$), fibrinogen ($\ge 150\,\text{mg}$), von Willebrand factor (vWF), Factor XIII, and fibronectin.

RBC Storage Lesion

The constellation of biochemical changes occurring in red blood cells stored at $1^\circ\text{C}-6^\circ\text{C}$, including decreases in pH, ATP, 2,3-DPG, and sodium, alongside increases in plasma potassium, ammonia, and free hemoglobin.

Blood Component Irradiation

A gamma- or X-ray treatment (minimum $25\,\text{Gy}$ to container midplane) that inactivates donor T-lymphocytes' ability to divide, preventing Transfusion-Associated Graft-versus-Host Disease (TA-GVHD).

Leukocyte Reduction

A filtration process that reduces residual white blood cells to $< 5 \times 10^6$ per unit while retaining at least $85\%$ of original RBCs; prevents febrile nonhemolytic reactions, CMV transmission, and HLA alloimmunization.

Coombs Check Cells

Commercially prepared IgG-sensitized red blood cells added to all negative indirect and direct antiglobulin tests to confirm that antihuman globulin reagent was added, unneutralized, and functionally active.

Elution

A laboratory procedure that physically or chemically dissociates bound antibodies from sensitized red blood cells into a fluid supernatant (eluate) to identify antibody specificity.

Adsorption

A blood bank technique using antigen-positive intact red blood cells to bind and remove specific antibodies from serum or plasma.

Donath-Landsteiner Antibody

A biphasic IgG autoantibody with autoanti-P specificity associated with paroxysmal cold hemoglobinuria (PCH) that fixes complement at $4^\circ\text{C}$ and lyses red cells when warmed to $37^\circ\text{C}$.

Kleihauer-Betke Test

An acid-elution cytochemical stain that differentiates fetal from adult hemoglobin based on fetal hemoglobin's resistance to acid elution; quantifies fetomaternal hemorrhage via the formula: $\text{KB}\% \times 50 = \text{mL of whole blood bleed}$.

Rosette Test

A qualitative screening test for fetomaternal hemorrhage that detects D-positive fetal cells in maternal D-negative circulation at volumes as low as $10\,\text{mL}$.

Rh Immune Globulin (RhIG)

Purified anti-D antibodies administered to nonsensitized Rh-negative individuals; a standard $300\,\mu\text{g}$ dose suppresses alloimmunization to up to $30\,\text{mL}$ of fetal whole blood ($15\,\text{mL}$ of packed red cells).

Transfusion-Related Acute Lung Injury (TRALI)

A life-threatening complication occurring within 6 hours of transfusion, caused by donor anti-HLA or antineutrophil antibodies triggering recipient granulocyte activation and noncardiogenic pulmonary edema.

Transfusion-Associated Circulatory Overload (TACO)

A nonimmune adverse transfusion reaction resulting from rapid or excessive volume administration, marked by hypertension, tachycardia, dyspnea, and cardiogenic pulmonary edema.

Mixed-Field Agglutination

A serological pattern demonstrating distinct clumps of agglutinated cells surrounded by unagglutinated cells, indicating the presence of two separate cell populations.

High Titer, Low Avidity (HTLA) Antibodies

Alloantibodies directed against high-incidence antigens (such as Chido and Rodgers) that characteristically exhibit weak reactivity that persists unchanged even across high serum dilutions.