1. The specific reaction pattern of red blood cells of an individual to the antisera of one blood group as, for example, of the ABO blood group, which consists of four major blood types, O, A, B, and AB.
2. A blood type is a description an individual's characteristics of red blood cells due to substances (carbohydrates and proteins) on the cell membrane. The two most important classifications to describe blood types in humans are ABO and Rh factor. There are 46 other known antigens, most of which are much rarer than ABO and Rh. blood transfusions from incompatible groups can cause an immunological transfusion reaction , resulting in hemolytic anemia, renal failure, shock, and death.