Annabelle Breakey/Getty Images

Blood is the lifeblood of the human body, circulating oxygen, nutrients, and hormones while supporting the immune system and clearing waste. Among the many blood types, Rhnull stands out as the most elusive, earning the nickname “golden blood.” Understanding its rarity requires a brief look at how blood types are determined.

Blood types are classified by the presence or absence of antigens—proteins on the surface of red blood cells that the immune system can recognize as foreign. The classic eight blood types (A+, A–, B+, B–, AB+, AB–, O+, O–) reflect the ABO system combined with the Rh factor, where RhD is the most common antigen tested. Most people are either RhD positive or negative.

Rhnull is unique because its red blood cells lack *all* Rh antigens. Cleveland Clinic transfusion medicine physician Zaher Otrock explains, “We test for RhD because it’s the one most likely to trigger an immune reaction… but it’s definitely not the only one to consider.” The absence of any Rh antigens makes Rhnull exceptionally rare and medically significant.

What It Means to Have Rhnull Blood

Until 1961, the lack of antigens in Rhnull was thought to be a death sentence. The discovery of an indigenous Australian woman with the type proved otherwise. Since then, fewer than 50 individuals worldwide have been identified with Rhnull.

Transfusions with Rhnull blood pose both advantages and challenges. Because the cells carry no antigens, Rhnull donors are universal donors for other rare Rh blood types, much like O– blood can be used for any common type. However, individuals with Rhnull can only safely receive Rhnull blood; exposure to other types can trigger severe immune reactions.

American Rare Donor Program director Sandra Nance notes, “There are nine active donors in the whole community of rare blood donors.” Dr. Otrock advises that Rhnull carriers consider donating and freezing their blood for planned surgeries and managing anemia with iron or folic acid to reduce transfusion needs.

In a related rarity, a woman with the Gwada negative type—currently the only known individual with that blood—illustrates the extreme specificity of these rare types. The scientist who identified her noted she is “the only person in the world who is compatible with herself.”

Rhnull remains one of the most fascinating and critical subjects in transfusion medicine, underscoring the importance of rare blood donor programs and ongoing research into antigen compatibility.