The Rarest Blood Type

The rarest known blood type is Rh-null, informally called "golden blood." It is defined by the complete absence of all antigens in the Rh blood-group system, whereas even people who are "Rh negative" still carry other Rh antigens. Since it was first described in 1961, only around 43 individuals have ever been documented with it, and far fewer are active blood donors.

Rh-null is prized medically because it can, in principle, be given to patients with any rare Rh type, making it a universal donor within the Rh system. But that same rarity is a danger to the people who have it: if they need a transfusion, compatible blood is extraordinarily hard to source and must often be shipped internationally from the tiny pool of known donors. By comparison, common types such as O-positive are shared by billions of people.