Which blood type is recognized as the universal donor?

The designation of O negative as the universal donor blood type is primarily due to the absence of A, B, and Rh antigens on the surface of its red blood cells. This means that O negative blood can be transfused to individuals with any blood type without the risk of agglutination or an immune response. When someone receives blood, their immune system may recognize foreign antigens as a threat, leading to potential complications. Since O negative lacks these antigens, it is compatible with all other blood types, making it a safe choice in emergency situations where the blood type of the recipient is unknown.

In contrast, other blood types contain either A or B antigens, or both, which can provoke an immune reaction if transfused to a person whose blood does not match those antigens. For example, AB positive carries both A and B antigens and can only donate to AB positive, AB negative, A positive, A negative, B positive, and B negative recipients, limiting its universal applicability. Similarly, A positive and B positive blood types have their specific antigen profiles that restrict their use in transfusion scenarios. Therefore, O negative remains the preferred type for universal donation.