Which blood type is known as the universal donor?

The blood type known as the universal donor is O negative. This designation is attributed to the absence of A and B antigens on the surface of O negative red blood cells. Because these antigens are what trigger immune responses during blood transfusions, having none means that O negative blood can be given to individuals with any other blood type without the risk of an adverse reaction due to blood type incompatibility.

In contrast, blood types like A positive, B negative, and AB positive contain specific antigens that can provoke immune responses in patients receiving transfusions who do not have the same blood type. Therefore, while these types can be given to matching recipients, they cannot be considered universal donors. O negative is crucial in emergency situations where there is no time for blood typing, enabling medical professionals to provide safe blood transfusions to patients of any blood type.