Which blood type is the universal donor for red blood cells?

• A. O Negative
• B. A Positive
• C. AB Positive
• D. B Negative

Answer: (A)

Universal donor for red blood cells means donor cells that can be given to anyone without triggering an immune reaction. This requires red cells that lack A and B antigens as well as the Rh D antigen. Type O negative fits this perfectly because its red blood cells have no A or B antigens and are Rh negative. That combination makes it compatible with recipients of any ABO/Rh type, which is why it’s used in emergencies when the patient’s blood type is unknown. Other blood types carry A or B antigens or the Rh antigen, so they can cause reactions in recipients who don’t have those antigens and aren’t universally compatible.