Why is type O negative often called the universal donor for blood transfusions?

• A. O positive red blood cells have A antigens.
• B. O negative red blood cells have no A or B antigens and can be given to anyone.
• C. AB negative blood has no A or B antigens and can be given to anyone.
• D. O negative red blood cells have A antigens.

Answer: (B)

Universal donor status for blood transfusions comes from compatibility between donor red blood cell antigens and the recipient’s antibodies. Type O negative red blood cells lack the A and B antigens on their surface and are also Rh negative, so they are unlikely to be targeted by recipients’ anti-A, anti-B, or anti-D antibodies. That means they can be given to people of almost any ABO and Rh type in emergencies.

The statement that O negative red blood cells have no A or B antigens and can be given to anyone is the best reflection of this idea. The other options misstate which antigens are present or imply the wrong compatibility, so they don’t describe why O negative is the universal donor.