Q**You recently said people with Type O blood are universal donors. Isn't it true that the use of O, Rh positive blood in an Rh negative recipient, can create problems?
Type O individuals are universal donors only with respect to the AB blood group antigens. Recipients of a blood transfusion, especially those who have had prior transfusions, may have produced antibodies against one or more of the many other antigens that can be present on the red cells of the transfused blood and lead to serious reactions.
The most potent of the other antigens on red cells is the Rh antigen D. Individuals are termed Rh positive when their red cells contain this antigen.