Your Blood type is a powerful genetic fingerprint that identifies you as surely as your DNA. A blood type/group is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells. These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system. A total of 30 human blood group systems are now recognized by the International Society of Blood Transfusion. The ABO and Rh systems are the most commonly used.