Final answer:
More than 50 blood antigens exist, but the ABO and Rh blood groups are the most significant for blood transfusions. The ABO blood group has types A, B, AB, and O, with type O negative blood considered the universal donor due to the absence of A and B antigens.
Step-by-step explanation:
Over 50 blood antigens have been identified on the membranes of erythrocytes, which are red blood cells. However, the most significant and widely considered blood antigens in terms of transfusion medicine and potential harm to patients are the ones in the ABO blood group and the Rh blood group. The ABO blood group system is characterized by the presence or absence of two antigens, A and B, which are glycoproteins. A blood type A individual has A antigens, blood type B has B antigens, blood type AB carries both A and B antigens, and blood type O carries neither antigen, which is why type O negative blood is referred to as the universal donor. The Rh blood group is another significant blood group often considered in transfusions due to the presence or absence of the Rh factor, also known as the D antigen.