ABOveriryhmän

ABOveriryhmän, the Finnish term for the ABO blood group system, is the classification of human blood based on the presence or absence of A and B antigens on red blood cells. The system includes four main serotypes: A, B, AB, and O.

Antigens, antibodies and compatibility are central to the ABO system. Individuals produce naturally occurring antibodies against the ABO antigens they do not express. Type A blood has anti-B antibodies, type B has anti-A, type AB has neither anti-A nor anti-B antibodies, and type O has both. The H antigen serves as a common precursor for A and B antigens; a rare Bombay phenotype lacks H antigen and therefore does not express A or B antigens even if the genotype would predict them.

Genetics and expression involve the ABO gene on chromosome 9, which encodes glycosyltransferases that modify the H antigen to form A or B antigens. The O allele results in an inactive enzyme, leaving the unmodified H antigen. Inheritance is codominant, meaning A and B alleles can both be expressed in AB individuals, while O is recessive.

Clinical relevance is strongest in transfusion medicine and organ transplantation. Matching the ABO type between donor and recipient helps prevent acute hemolytic reactions. Incompatibilities can cause serious complications. In pregnancy and transplantation, careful antigen compatibility testing reduces risk of immunological complications.

Typing methods include traditional serology, which uses agglutination testing, and increasingly molecular typing for more precise determination of ABO status. The ABO system remains one of the most important and routinely used classifications in medicine.

See also: Rh factor, crossmatching, transfusion medicine.