blood types

Blood types are classifications of blood based on the presence or absence of specific antigens and antibodies. The main blood group systems are ABO and Rh. The ABO system has four types: A, B, AB, and O, determined by antigens on red blood cells. The Rh system adds a positive (+) or negative (-) designation based on the presence of the Rh factor. For example, A+ has A antigens and the Rh factor, while O- lacks A, B antigens, and the Rh factor. Blood type compatibility is crucial for blood transfusions and organ transplants to avoid immune reactions.