What type of blood is considered the universal donor?

The designation of O negative blood as the universal donor is based on the absence of A and B antigens on the surface of the red blood cells. This means that O negative blood can be transfused into individuals of any blood type without the risk of an adverse immune response, making it incredibly valuable in emergency situations where there might not be time to type the recipient's blood.

In contrast, other blood types contain specific antigens that can trigger immune reactions in recipients who have different blood types. For example, A positive blood has A antigens and can cause complications when given to someone with a different blood type. The same goes for B negative and O positive, which also carry antigens that must be matched with the recipient's blood type to prevent potential hemolytic reactions. Therefore, O negative is universally accepted for transfusions, particularly in emergencies.