One of the rarest blood types in the world is Rhnull, sometimes referred to as "golden blood."
One of the rarest blood types in the world is Rhnull, sometimes referred to as ‘golden blood’. People with this blood type have a complete absence of any of the Rh antigens. It was first discovered in an Aboriginal Australian and is extremely rare, with fewer than 50 individuals known to have Rhnull blood in the 50 years after its discovery. Its rarity means that donations of Rhnull are incredibly scarce and difficult to obtain when a Rhnull individual needs a blood transfusion, relying on the cooperation of a small network of regular Rhnull donors around the world to ensure this blood type is always available when needed.
Interestingly, for reasons that aren’t well understood by scientists, not all ‘foreign’ antigens are equally likely to be targeted for destruction by antibodies. So, although there are 36 recognized blood group systems in total, there are only certain types that doctors and patients need to be careful about when it comes to blood transfusions. AB0 antibodies, for example, are pretty much always clinically significant. Other blood groups that are likely to cause transfusion reactions include the blood types MNS, Kell, Kid, and Duffy.