Which blood type is the universal donor?

• A. Type AB
• B. Type O
• C. Type A
• D. Type B

Answer: (B)

Red blood cell transfusion compatibility hinges on avoiding A or B antigens that a recipient’s plasma antibodies would attack. Type O red blood cells have neither A nor B antigens on their surface, so they won’t provoke anti-A or anti-B antibodies in recipients of any ABO type. If you also consider Rh, type O negative lacks the D antigen, making it safe to transfuse to patients of any Rh status in emergencies. That combination makes type O (especially O negative) the universal donor for red blood cells. For plasma transfusions, note that AB plasma is the universal donor because it contains no anti-A or anti-B antibodies.