Blood typing is the immunohematological classification of erythrocytes by the presence or absence of inherited surface antigens — the A and B antigens of the ABO system and the D (Rh) antigen of the Rh system — where each antigen is the product of a specific gene expressed on the red blood cell membrane. The governing principle (Landsteiner's rule) is that plasma contains naturally occurring antibodies against whichever ABO antigens the individual lacks, so contact between an antigen and its complementary antibody produces agglutination, the clumping of red cells that underlies both laboratory typing and transfusion incompatibility; Rh antibodies differ in that they are not naturally present but are formed only after sensitizing exposure to Rh-positive cells. This concept belongs to hematology and transfusion medicine within physiology and immunology, and it links antigen–antibody recognition theory to the clinical rules of donor–recipient compatibility and to maternal–fetal alloimmunization.
Blood typing is the immunohematological classification of erythrocytes by the presence or absence of inherited surface antigens — the A and B antigens of the ABO system and the D (Rh) antigen of the …