Among the eight common blood types, AB negative is the rarest, found in less than 1% of the population. In the United States, only about 0.6% of people carry AB negative blood. But the full picture of blood type rarity goes well beyond the familiar ABO system, extending into ultra-rare categories that affect fewer than 50 known people on Earth.
AB Negative: The Rarest Common Blood Type
Blood typing uses two systems together: the ABO group (A, B, AB, or O) and the Rh factor (positive or negative). Combining these produces eight standard types. Here’s how they break down in the U.S. population, according to Stanford Blood Center:
- O positive: 37.4%
- A positive: 35.7%
- B positive: 8.5%
- AB positive: 3.4%
- O negative: 6.6%
- A negative: 6.3%
- B negative: 1.5%
- AB negative: 0.6%
UK data from NHS Blood and Transplant tells a similar story, with AB negative at roughly 1% of donors. The pattern holds across most populations of European descent: AB negative consistently sits at the bottom.
Why AB Negative Is So Uncommon
Two genetic events have to line up for someone to be AB negative, and both are individually unlikely. First, the person needs one A allele from one parent and one B allele from the other. Since A and B are each less common than O in most populations, inheriting both is already unusual. Second, they need to be Rh negative, which requires getting the recessive Rh-negative gene from both parents. The Rh-positive gene is dominant, so a person only needs one copy of it to test positive. Being Rh negative requires two copies of the recessive version.
The combination of these two low-probability events is what makes AB negative so scarce. It’s essentially a genetic parlay: you need the least common ABO pairing and the less common Rh result at the same time.
Blood Types Rarer Than AB Negative
The eight standard types are just the beginning. Beyond ABO and Rh, red blood cells carry more than 600 known antigens, surface markers that the immune system uses to distinguish “self” from “foreign.” The American Red Cross defines a blood type as rare when a person lacks an antigen that 99% of people carry. If they lack one that 99.99% of people carry, their blood is classified as extremely rare.
Several of these rare types cluster in specific ethnic and regional populations. Among African Americans, U-negative and Duffy-negative blood types are recognized as uncommon phenotypes. Pacific Islander and Asian populations have higher rates of a type called Jk(a-b-). Hispanic populations may carry Di(b-), while people of East European or Russian Jewish descent occasionally have Dr(a-). Native American and Alaskan Native populations carry a rare type known as RzRz. These aren’t exotic curiosities. They create real challenges when someone with one of these types needs a transfusion, because the matching donor pool is tiny and often limited to people of the same background.
The Bombay Phenotype
One especially tricky rare type is the Bombay phenotype, sometimes written as hh. People with this blood type are missing a foundational molecule called the H antigen, which is the building block the body uses to create A and B antigens. Without it, their blood looks like type O on a standard test, but it isn’t. If they receive regular type O blood, their immune system attacks it because it recognizes the H antigen as foreign.
The Bombay phenotype occurs in about 1 in 10,000 people in India and Southeast Asia and roughly 1 in 250,000 among Caucasian populations. People with this type can only receive blood from other Bombay phenotype donors. Misidentification can trigger a fatal transfusion reaction, which is why blood banks increasingly recommend reverse-grouping confirmation as a standard screening step.
Rh-Null: Golden Blood
The rarest blood type ever documented is Rh-null, sometimes called “golden blood.” People with Rh-null lack all of the Rh antigens on their red blood cells, not just the main one that determines positive or negative status. Only about 43 people have ever been identified worldwide with this type, according to Cleveland Clinic.
The nickname “golden blood” comes from its extraordinary value in transfusion medicine. Because Rh-null blood has no Rh antigens at all, it can theoretically be given to anyone with rare Rh types without triggering an immune response. That makes each Rh-null donor incredibly important. But the flip side is brutal: if a person with Rh-null blood needs a transfusion themselves, they can only receive Rh-null blood from one of the handful of other people in the world who share their type.
How Rare Blood Gets Matched
For people with rare blood types, finding a match in an emergency is a logistical challenge that can cross international borders. In the United States, the American Rare Donor Program maintains a database of roughly 51,000 active donors with rare phenotypes. The program ships about 1,800 rare blood units per year for transfusions across the country, operating around the clock. When a hospital identifies a patient with an unusual antibody profile, it sends a request to the program’s hub in Philadelphia, which searches the database and contacts facilities with registered matching donors.
Even with this system, supply doesn’t always meet demand. A study of requests for high-incidence antigen-negative blood for sickle cell disease patients found that 88% of requests were completely or partially filled, meaning about 1 in 8 went unfilled. The cost is significant too. Special antigen typing and search fees can add $500 to $1,200 per unit on top of the normal cost of blood. When domestic searches come up empty, the program initiates international searches, reaching out to rare donor registries in other countries.
For people with the rarest types, like Rh-null or the Bombay phenotype, some doctors recommend banking their own blood in advance of any planned surgery. It may be the only reliable supply available.
Why Rarity Varies by Region
Blood type distribution isn’t uniform across the globe. O positive dominates worldwide, but the frequencies of other types shift dramatically depending on ancestry. The Rh-negative gene, for instance, is most common in people of European descent (which is why O negative runs around 14% in the UK but is much rarer in East Asian populations). Type B is more prevalent in Central and South Asia than in Europe or the Americas.
This means a blood type that’s rare in one country might be less unusual in another. AB negative is the rarest of the eight standard types almost everywhere, but the degree of its rarity depends on the local population’s genetic makeup. And the 600-plus additional antigens create a patchwork of regional rarity that standard ABO/Rh typing doesn’t capture at all. Two people who are both “O positive” on a basic test might still be incompatible if one carries a rare antigen the other lacks antibodies for.
This is why blood donation from diverse communities matters so much. The more genetically varied the donor pool, the better the odds of finding a match for patients with unusual blood types.