Which blood type is known as the universal donor?

The designation of O negative blood type as the universal donor comes from its unique characteristics regarding the presence of antigens. Individuals with O negative blood do not have A or B antigens on their red blood cells, and they also lack the Rh factor, which is what typically distinguishes positive from negative blood types. This means that when O negative blood is transfused into a recipient, their immune system is less likely to react negatively against it since there are no antigens to provoke an immune response.

In contrast, other blood types such as A, B, or AB have specific antigens that could trigger reactions in recipients who do not have the corresponding type. For example, A type blood has A antigens, B type has B antigens, and AB type has both. Therefore, if a person with a different blood type receives A or B blood, they may experience a serious transfusion reaction.

The ability of O negative blood to be safely given to any patient in need of a transfusion makes it invaluable, particularly in emergency situations when there may not be time to determine a person's blood type.