The Rhnull blood type is a rare blood group characterized by the complete lack of antigens in the Rh system, which is the largest blood group system. It is so rare that only about 43 people on Earth have ever been reported to have it, and there are only nine active donors
. This blood type is associated with chronic hemolytic anemia of varying degrees, and individuals with Rhnull syndrome readily form alloantibodies when exposed to Rh antigens
. Due to its rarity, Rhnull blood is extremely valuable for scientific research and blood transfusions, as it lacks common antigens and can be accepted by anyone who needs a transfusion without the risk of a blood transfusion reaction
