How is blood type determined?

Blood type is determined by the presence or absence of specific antigens on the surface of red blood cells. These antigens, which can be proteins or carbohydrates, are inherited traits that play a crucial role in the immune system's recognition of the body's own cells versus foreign cells. The classification of blood types, such as A, B, AB, and O, is based specifically on which antigens (A or B) are present on the red blood cells. For instance, type A blood has A antigens, type B has B antigens, type AB has both, and type O has neither.

This understanding is crucial because it informs practices like blood transfusions and organ transplants, where compatibility between donor and recipient blood types must be established to prevent adverse immune reactions. The other factors mentioned, such as hemoglobin levels, total blood volume, or white blood cell counts, do not play a direct role in defining blood type. Instead, these parameters may provide information about overall health or specific conditions but are not involved in the classification of blood types.