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, Director of the National Immunohematology Reference Laboratory in Paris, told Mosaic.
Besides making someone feel really special, Rhnull or other rare bloods are extremely valuable. "Because Rhnull blood can be considered 'universal' blood for anyone with rare blood types within the Rh system, its life-saving capability is enormous. As such, it's also highly prized by doctors – although it will be given to patients only in extreme circumstances, and after very careful consideration, because it may be nigh on impossible to replace," Mosaic reports.