Which blood type is commonly called the universal red-cell donor?

O negative is commonly called the universal red-cell donor because its red blood cells lack A, B, and RhD antigens. This makes them less likely to trigger an immediate immune reaction when transfused into people with other blood types.

The ABO blood-group system classifies blood according to A and B antigens on red blood cells. The Rh system mainly refers to the presence or absence of the D antigen: people with it are Rh-positive, while those without it are Rh-negative. O-negative blood lacks all three major antigens used in this basic compatibility rule.

Hospitals often reserve O-negative red cells for emergencies when a patient's blood type is not yet known, including severe trauma. It is not a universal donor for every blood product: plasma compatibility follows different rules, and laboratory testing remains important whenever there is time. O-negative people can generally receive only O-negative red cells, which is why this blood type is especially valuable in blood-bank inventories.