The rarest blood type in the world is RH-null blood also known as 'Golden Blood'. It is only been identified in 43 people during the last 50 years.
The rarest blood type in existence is Rhnull blood. This stuff is characterized by a complete lack of antigens in the Rh system, which is the largest blood group system.
This includes the D antigen (Rh factor, baby), plus the other 50-something antigens in the group. This blood type is so rare that only 43 people on Earth have ever been reported to have it, and there are only nine active donors.
Until 1961, doctors assumed a person lacking all Rh antigens would never even make it out of the womb alive. "It's the golden blood," Dr. Thierry Peyrard, the Director of the National Immunohematology Reference Laboratory in Paris, told Mosaic.
Source: discovery.com
