Which blood type is considered a universal donor?

The designation of a blood type as a universal donor refers to the compatibility of that blood type with all other blood types during transfusions. O- (O negative) is considered the universal donor blood type because it lacks the A and B antigens found on the surface of red blood cells, as well as the Rh factor, which is the D antigen.

When transfusing blood, the recipient’s immune system can react to any foreign antigens present in the donor blood. Since O- type blood has no A, B, or Rh antigens, it can be safely given to recipients of any blood type without causing an immune response. This characteristic makes O- blood particularly valuable in emergency situations where there may not be time to match a patient’s blood type precisely.

In contrast, other blood types contain specific antigens that can trigger immune reactions if transfused into an incompatible recipient. For instance, A+ blood has A antigens and may cause a reaction in someone with B or O blood type, while AB+ contains both A and B antigens. Therefore, while AB+ is actually the universal recipient (able to receive all blood types), O- remains the only blood type universally acceptable for donation.