Among the eight common blood types, AB negative is the rarest, found in roughly 1% of the population. But if you zoom out beyond the familiar A-B-O system, far rarer blood types exist. The rarest known is Rh-null, sometimes called “golden blood,” which has been documented in only about 43 people in recorded medical history.
AB Negative: The Rarest Common Type
Most people learn about blood types through the ABO and Rh system, which sorts blood into eight categories: A+, A−, B+, B−, O+, O−, AB+, and AB−. Of these, AB negative is the least common. Only about 1% of blood donors carry it, according to NHS Blood and Transplant data. AB positive is also uncommon at around 3 to 4%, but the negative version is consistently the hardest to find on blood bank shelves.
Your ABO type is determined by which sugar molecules sit on the surface of your red blood cells. Type A has one kind, type B has another, AB has both, and O has neither. The “positive” or “negative” label refers to a separate protein called the Rh D antigen. When you combine the least common ABO group (AB) with the less common Rh status (negative), you get a type that very few people carry.
Rh-Null: The True Rarest Blood on Earth
The ABO and Rh D system is just one layer of a much more complex picture. The International Society of Blood Transfusion currently recognizes 48 distinct blood group systems, each defined by different proteins or sugars on the red blood cell surface. When you account for all of these systems, some combinations become extraordinarily rare.
The most extreme example is Rh-null blood. While most people are simply “Rh positive” or “Rh negative” based on whether they have the Rh D protein, the full Rh system actually involves dozens of related antigens. People with Rh-null blood lack every single one of them. Fewer than 50 individuals have ever been identified with this type worldwide, earning it the nickname “golden blood.” That name doesn’t mean the blood is superior. It’s simply a way of conveying just how scarce it is.
Rh-null is inherited in an autosomal recessive pattern, meaning a person needs to receive the relevant genetic variant from both parents. Because carriers typically have no symptoms and normal-looking blood tests, the trait can pass silently through families for generations before two carriers happen to have a child together.
Living With Rh-Null Blood
Having golden blood isn’t just a curiosity. It comes with real health consequences. The Rh proteins play a structural role in red blood cells, helping maintain their shape and stability. Without any Rh antigens, red blood cells become misshapen and fragile. They break down faster than normal, which shortens their lifespan in the bloodstream and leads to mild chronic anemia in most cases. The National Institutes of Health lists associated features including abnormally shaped cells, increased fragility, and a higher-than-normal turnover of red blood cells.
The bigger challenge is what happens if someone with Rh-null blood needs a transfusion. Because their immune system has never encountered any Rh proteins, it can mount an aggressive response against virtually all donated blood. The only truly safe match is blood from another Rh-null donor, and with fewer than 50 known individuals on the planet, finding that match is an enormous logistical problem. Some blood services maintain frozen banks of rare blood types that can be stored for decades, but even these inventories require periodic review as testing standards evolve.
Other Exceptionally Rare Types
Rh-null gets the most attention, but other rare phenotypes create similar challenges. The Bombay blood type, for instance, is caused by a recessive genetic variant at a completely separate gene from the ABO system. People with Bombay blood appear to be type O on standard tests, but they actually lack a foundational molecule that types A, B, and O all share. This means they can only receive blood from other Bombay-type donors. It occurs in about 1 in 10,000 people in India and 1 in 8,000 in Taiwan, making it rare but far more common than Rh-null.
Duffy-null is another notable example. People who lack the Duffy protein on their red blood cells are most commonly found among populations with roots in sub-Saharan Africa, particularly Egypt, Zimbabwe, Kenya, Sudan, and Nigeria. This trait actually provides a degree of protection against certain types of malaria, which is likely why natural selection favored it in those regions. The Kidd-null phenotype, meanwhile, appears more frequently in people from the Philippines, New Zealand, Samoa, and Tonga.
These patterns matter in diverse societies. A 2024 study by Australian Red Cross Lifeblood found that as the country’s ethnic makeup shifted, so did the prevalence of lesser-known blood types among donors. Demand for Duffy-null and Kidd-null blood increased alongside immigration from regions where those types are more common, creating new pressure on blood banks to recruit donors with matching backgrounds.
Why Rare Blood Is Hard to Match
Finding compatible blood for someone with a rare phenotype is a multi-step challenge that starts with simply recognizing the problem. Standard blood typing only checks for ABO and Rh D. If a patient develops antibodies against a less common antigen after a previous transfusion or pregnancy, specialized reference labs must step in to identify exactly which protein is causing the reaction. This requires trained technicians and tools that many hospitals don’t have on-site, so samples often get referred to national or international reference laboratories.
Once the antibody is identified, blood services have to find a donor who lacks the corresponding antigen. That can mean screening thousands of donors or searching frozen rare-blood inventories. For some phenotypes, the right donor may not exist in the patient’s country at all, requiring international collaboration and shipment. The International Society of Blood Transfusion coordinates these cross-border efforts, connecting blood services across regions to locate compatible units.
People who are identified as having a rare blood type are typically contacted and educated about their status. They’re encouraged to donate regularly and are often enrolled in rare donor registries so they can be reached quickly when a matching patient appears. For the handful of Rh-null individuals worldwide, this creates an unusual situation: their blood is so universally compatible within the Rh system that it could theoretically help many patients, yet so scarce that every unit is precious.
How Blood Group Science Keeps Expanding
The 48 blood group systems recognized today didn’t all arrive at once. New ones are still being identified as genetic tools improve. In 2022, the ISBT ratified the Er blood group system, the 43rd at the time, after researchers linked it to a protein involved in red blood cell structure. Antibodies against certain Er antigens had already been connected to severe complications in pregnancies, but the molecular basis wasn’t fully understood until modern gene-sequencing techniques made it possible.
Each new system means new rare phenotypes to catalog and new patients who might need specialized blood products. It also means that the answer to “what is the rarest blood type” will continue to evolve. For now, among the types your doctor routinely tests for, AB negative holds that title. In the broader world of blood immunology, Rh-null remains the rarest type ever documented in a living person.