Although more than 400 blood groups have been identified,the ABO blood group system remians the mostimpoant in clinical medicne because :
. ABO(H) antibodies are invariably present in plasma when persons RBC lacks the corresponding antigen
It was the first blood group system to be discovered
It has four different blood groups A,B, AB, O (H).
ABO(H) antigens are present in most body tissues and fluids.
ABO(H) antibodies are invariably present in plasma when persons RBC lacks the corresponding antigen