Which blood group is considered the universal donor?

The universal donor blood group is O negative (O-). This designation arises from the presence or absence of specific antigens on the red blood cells. Individuals with O negative blood do not have A, B, or Rh antigens, which means their blood can be transfused to any recipient without the risk of an immune reaction. In transfusion practices, compatibility between donor and recipient blood types is crucial; the absence of antigens makes O negative blood universally acceptable, as it will not trigger an immune response in recipients with any other blood type.

The other blood groups contain one or more antigens that can lead to allergic reactions or immune responses in recipients with different blood types, thereby limiting their use as universal donors. While AB positive blood types have all the necessary antigens to receive blood from all types, they cannot donate universally due to the presence of these antigens. Similarly, A positive and B negative blood types have specific antigens that could cause reactions in certain recipients, hence they cannot be considered universal donors.