A, B, AB, O blood groups

Blood groups A, B, AB, and O are classifications based on the presence or absence of specific proteins called antigens on the surface of red blood cells. Group A has A antigens; B has B antigens; AB has both, and O has neither. These antigens determine compatibility for blood transfusions and are inherited genetically. Additionally, blood may have antibodies against the antigens it lacks, which can cause reactions if mismatched. Understanding blood type is essential for safe transfusions and pregnancy considerations.