Universal blood donor type: Is there such a thing?

There is no universal blood donor type. Donated blood is routinely classified by type as A, B, AB or O, and as Rh positive or Rh negative. In the past, people with Type O/Rh negative blood were considered universal blood donors. This implied that anyone, regardless of blood type, could receive Type O/Rh negative blood without risking a transfusion reaction.

But scientists now have a much better understanding of the complex issues related to reactions to incompatible blood donor types. Even donors with Type O/Rh negative blood may have antibodies in their blood that cause serious reactions.

Before a blood transfusion, small samples of the recipient's and donor's blood are mixed to check compatibility. Doctors refer to this as crossmatching. Despite all such precautions, adverse transfusion reactions may still occur.