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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 compatibility of blood for transfusion.
(Medicine) a system for classifying human blood on the basis of the presence or absence of two antigens on the red cell membrane: there are four such blood types (A, B, AB, and O)
a classification of human blood into four major groups, A, B, AB, and O, based on the presence on the surface of red blood cells of either of two antigens, A or B, or their absence, O: used in determining compatibility for transfusions.