Which blood type is known as the universal donor?

The blood type known as the universal donor is O. This designation arises because individuals with type O blood have neither A nor B antigens on the surface of their red blood cells. As a result, type O blood can be transfused to patients of any other blood type without the risk of an immune reaction caused by incompatible antigens.

In transfusion medicine, the presence of A and B antigens can trigger an immune response if blood with incompatible antigens is introduced to a recipient. Because type O blood lacks these antigens, it is safe for universal transfusion, making it crucial in situations where the recipient’s blood type is unknown. This quality has made O type essential for emergency transfusions, where time is of the essence.

Other blood types have specific antigen presentations that could lead to reactions if given to someone with a different type, which is why they are not classified as universal donors.