Why can you not get blood transfusions from all the blood groups?

Blood transfusions must be compatible to prevent adverse reactions. Each blood group is determined by specific antigens on the surface of red blood cells; if a person receives blood with incompatible antigens, their immune system may attack the transfused blood, leading to serious complications. The main blood groups—A, B, AB, and O—along with the Rh factor (positive or negative) dictate compatibility, making it crucial to match donors and recipients accurately. This ensures the safety and effectiveness of the transfusion.