The “universal” blood type for red blood cell transfusions is type O negative (O−). This type lacks A, B, and Rh antigens on the red blood cells, so it is least likely to trigger an immune reaction in someone whose blood type is unknown in an emergency. For completeness:
- Universal red blood cell donor: O negative (can be given to almost anyone in urgent situations).
- Universal plasma donor: AB (AB plasma can usually be given to people of any ABO type).