ABOblodtyper

ABOblodtyper, or the ABO blood type system, classify human blood by the presence or absence of A and B antigens on the surface of red blood cells. The A and B antigens are produced by codominant IA and IB alleles, while the i allele represents O (no A or B antigen). Common phenotypes are type A (IAIA or IAi), type B (IBIB or IBi), type AB (IAIB), and type O (ii).

In addition to red cell antigens, the plasma of individuals contains naturally occurring antibodies against the other ABO antigens. Type A individuals usually have anti-B antibodies; type B individuals have anti-A; type AB individuals have neither, and type O individuals have both anti-A and anti-B. These antibodies can cause agglutination and hemolysis if blood of a different ABO type is transfused.

The ABO genes are located on chromosome 9, and the system is central to transfusion medicine. The distribution of ABO types varies by population and geography; some types are more common in certain groups than in others. ABO antigens are also present on other tissues, and the presence or absence of these antigens can influence transfusion and transplantation considerations beyond red cells.

Clinically, ABO typing is essential for safe transfusion. Matching ABO status (and RhD) is standard; type O red cells are often used in emergencies as a universal donor, while type AB plasma is used as a universal donor for plasma transfusions. ABO incompatibility can contribute to pregnancy complications, including hemolytic disease of the fetus and newborn, though Rh incompatibility remains a major factor in that condition.

Typing methods include forward typing (testing red cells with anti-A and anti-B sera) and reverse typing (testing plasma with known A and B cells). Genotyping can supplement serology in complex cases.