•A person’s blood type is determined by the antigen on the surface of the RBC

•. There are four major ABO blood groups determined by the presence or absence of two red cell antigens (A and B).

•People who have neither A nor B antigens are classified as having type O blood.

•Those with A antigens are classified as having type A blood;

•those with B antigens, as having type B blood;

•and those with A and B antigens, as having type AB blood

•. The ABO blood groups are genetically determined.

• In the United States, types O and A are the most common.