ABO system

ABO system

n.

A classification system for human blood that identifies four major blood types based on the presence or absence of two antigens, A and B, on red blood cells. The four blood types (A, B, AB, and O, in which O designates blood that lacks both antigens) are important in determining the compatability of blood for transfusion.

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ABO system

ABO blood group system Transfusion medicine The major alloantigen system in humans, based on 3 carbohydrate antigens expressed on RBCs, encoded on chromosome 9q34 Significance ABO blood groups determine who can donate blood to, or accept blood from, whom; type A or AB blood causes an immune reaction in type Bs; type B and AB blood cause an immune reaction in type As; conversely, type O blood has no A or B antigens–type Os are universal donors; since AB blood already produces both antigens, type ABs can accept any of the other blood types without suffering an immune reaction, and are thus known as universal recipients, as he/she forms antibodies to neither A nor B antigens. See Blood group antigens, Lewis antigen, Transplantation, Universal donor, Universal recipient.