The rarest blood type in the world is Rh-null, sometimes called “golden blood.” Fewer than 50 people in recorded history have ever been confirmed to have it. But rarity depends on how you define it. Within the familiar ABO system most people know, AB-negative is the rarest, found in roughly 1% of the global population. Beyond ABO, dozens of other blood group systems create phenotypes so uncommon that finding a compatible donor can take an international search.
AB-Negative: The Rarest Common Blood Type
When most people ask about the rarest blood type, they’re thinking of the eight standard types: A+, A-, B+, B-, O+, O-, AB+, and AB-. Among those, AB-negative is the least common. About 1 in 100 blood donors carries it. Globally, the AB group as a whole accounts for only about 3% of the population, and adding the Rh-negative factor shrinks that number further.
For context, the global distribution of ABO blood groups breaks down roughly like this: type O at 47%, type A at 41%, type B at 9%, and type AB at 3%. Rh-negative status is itself uncommon, appearing in about 15% of people of European descent but far less frequently in Asian and African populations. So AB-negative sits at the intersection of two relatively rare traits.
Rh-Null: Golden Blood
Rh-null is in a category of its own. While most people are simply Rh-positive or Rh-negative (referring to one specific protein on the surface of red blood cells), the Rh system actually involves dozens of different proteins. People with Rh-null blood lack every single one of them. Only about 43 people have ever been documented with this phenotype, according to Cleveland Clinic.
The condition results from an extremely rare genetic mutation. It’s not inherited in a simple dominant or recessive pattern that runs through large families. Instead, the specific combination of mutations needed is so unlikely that cases appear scattered across unrelated populations worldwide.
Rh-null blood is medically extraordinary because it can be transfused to anyone who is Rh-negative, regardless of which specific Rh proteins they’re missing. That universal compatibility within the Rh system is what earned it the nickname “golden blood.” The flip side is grim for the people who have it: if they ever need a transfusion themselves, only another Rh-null donor will do. With fewer than 50 known cases globally, that’s a vanishingly small pool.
The Bombay Phenotype
Another contender for rarest blood type is the Bombay phenotype, sometimes written as Oh. People with this type appear to be type O on standard blood tests, but their blood is fundamentally different. They lack a precursor molecule that all other ABO types build upon, which means transfusing them with regular type O blood can trigger a dangerous immune reaction.
The Bombay phenotype occurs in about 1 in 10,000 people in India, where it was first identified, and roughly 1 in a million people in Europe. Like Rh-null individuals, people with Bombay blood can only receive transfusions from other Bombay donors, making emergency situations particularly high-stakes.
Blood Groups Beyond ABO and Rh
The International Society of Blood Transfusion currently recognizes 48 distinct blood group systems encompassing 398 different antigens. ABO and Rh are just two of those systems. Others, like Kell, Duffy, and Kidd, each have their own set of proteins on the red blood cell surface that can cause transfusion reactions if mismatched.
In the Kell system, for instance, about 4% of people carry the Kell-positive antigen, making it relatively uncommon. The Duffy system has particular relevance for people of African descent: Duffy-negative blood is common in African and African American populations but rare elsewhere. Similarly, U-negative blood is almost exclusively found in Black communities. These patterns mean that a blood type considered common in one population can be nearly impossible to find in another.
This is why donor diversity matters so much. People with sickle cell disease, who often need repeated transfusions, frequently carry blood types unique to African American populations. Finding compatible blood depends on having enough donors from the same ethnic background.
How Rare Blood Is Found and Stored
When someone has an extremely rare blood type, locating a compatible unit can become an international effort. The International Rare Donor Panel, established in 1965 through a joint initiative between the World Health Organization and the International Society of Blood Transfusion, maintains a database of rare blood donors from 27 countries. The panel also tracks inventories of frozen rare blood units stored in blood banks around the world. Access is restricted to medical professionals sourcing blood for clinical use.
Standard red blood cells stored in liquid form last between 21 and 42 days, depending on the preservative used. That shelf life is far too short for blood types that might only be needed once every few years. Rare units are instead frozen, which extends their viability dramatically. In one documented case, red blood cells negative for a rare Kidd system antigen were thawed and prepared for a patient after three years in frozen storage. The second unit, unused, was refrozen to preserve the scarce supply.
This freeze-and-wait approach is the only practical solution for the rarest phenotypes. A hospital can’t keep fresh Rh-null blood on the shelf when the entire known population of donors worldwide wouldn’t fill a small room.
Why Rarity Varies by Population
Blood type frequencies are shaped by genetics, geography, and evolutionary history. Type O is dominant in Central and South America, where some indigenous populations are nearly 100% type O. Type B is more common in Central and South Asia. Rh-negative blood is concentrated in Europe, particularly among Basque populations, and is rare in East Asia.
This means “rarest” is always relative to where you are. AB-negative is the rarest of the standard eight types globally, but in a specific Japanese hospital, B-negative might be harder to find. In sub-Saharan Africa, Rh-negative blood of any ABO type is scarce. The practical challenge isn’t just how rare a blood type is worldwide, but how rare it is in the local donor pool when a patient needs it.