ABO Discrepancies and Phenotypes

Practice vocabulary and concepts related to ABO blood typing discrepancies, specialized phenotypes like Bombay, and corrective laboratory techniques.

Advanced age ABO discrepancy

A discrepancy characterized by missing or weak antibodies due to a patient's age, resolved by incubating forward and reverse tubes at $4\,^{\circ}\text{C}$ with an auto control to enhance naturally occurring cold ABO antibodies.

Anti-A1 alloantibody

An antibody developed by individuals who lack the A1 antigen structure (often classified as A2), which reacts with reagent A1 cells during reverse grouping.

Rouleaux formation

Pseudoagglutination caused by elevated plasma proteins that results in the stacking of red blood cells, appearing as a false-positive reaction in blood typing.

Saline replacement technique

A procedure used to resolve discrepancies caused by elevated plasma proteins (Rouleaux) by dispersing protein-induced stacking without disrupting true antibody-mediated agglutination.

Bombay Phenotype ($O_h$)

A rare phenotype that lacks the H antigen entirely; individuals possess naturally occurring Anti-A, Anti-B, and Anti-H in their serum, causing strong reactions with all reagent cells, especially Group O cells.

Ulex europaeus lectin

The source of Anti-H lectin, used to differentiate the Bombay phenotype (0 reaction) from standard Group O individuals (positive agglutination).

Anti-H in Group A1 individuals

An antibody produced by strong Type A1 individuals who convert nearly all H substance into A antigens; their serum reacts with commercial O cells (highest H density) but not their own cells.

Neonatal reverse typing discrepancy

A total lack of expected reverse reactions in newborns because their immune systems have not yet been exposed to environmental bacteria/food that stimulate ABO antibody production.

A2B individual

An individual who forward types as AB but displays a $1+$ reaction with A1 cells in reverse grouping due to the absence of the A1 antigen and the formation of an allo-Anti-A1.

Cold-reacting autoantibody

An autoantibody that reacts optimally at room temperature or lower; its interference in ABO typing is resolved by pre-warming patient serum and reagent cells to $37\,^{\circ}\text{C}$ before testing.

Dolichos biflorus lectin

A reagent used as Anti-A1 lectin to identify the presence of the A1 antigen.

Alpha-2-L-fucosyltransferase

The enzyme responsible for producing the H antigen; its absence is characteristic of the Bombay phenotype.