Of the eight common blood types, O+ is the most prevalent and AB- is the rarest. In the United States, about 37% of the population is O+, while only around 1% is AB-. But rarity depends heavily on where you live and your ethnic background, so the numbers shift significantly across different populations.
How Common Each Blood Type Is
Blood type is determined by two things: the ABO group (A, B, AB, or O) and the Rh factor (positive or negative). Combining these gives eight standard types. Here’s how they break down in the general U.S. population:
- O+: ~37%
- A+: ~36%
- B+: ~8%
- AB+: ~3%
- O-: ~7%
- A-: ~6%
- B-: ~1.5%
- AB-: ~0.6%
Roughly 82% of people in the U.S. are Rh-positive, which is why the negative versions of every blood type are less common than their positive counterparts. In the UK, the pattern is similar: about 48% of the population is type O overall, and around 85% are Rh-positive. O+ is the single most common type there at about 35%.
Why Rarity Changes by Ethnicity
Blood type frequencies vary dramatically across racial and ethnic groups. Among Hispanic Americans, 56.5% are type O, compared to 50.2% of Black Americans and a lower percentage of white Americans. Asian Americans, meanwhile, have a notably higher proportion of type B and AB blood.
The differences become even more striking with Rh-negative blood. White Americans are Rh-negative about 17.3% of the time, roughly two to three times the rate seen in Hispanic (7.3%) and Black (7.1%) populations. Among Asian Americans, Rh-negative blood is extremely uncommon, with O- found in just 0.7% of this group. This means that finding a compatible Rh-negative donor is much harder for some communities than for others, a persistent challenge for blood banks serving diverse populations.
What Determines Your Blood Type
Your blood type comes from a single gene with three possible versions, or alleles: A, B, and O. You inherit one allele from each parent, giving six possible genetic combinations that produce the four blood types. A and B are codominant, meaning if you inherit one of each, both are expressed and your blood type is AB. The O allele is recessive. It produces no surface marker on red blood cells, so you need two copies of O to be type O. If you have one A and one O allele, your blood type is simply A.
The Rh factor works separately. The gene for Rh-positive is dominant, so you only need one copy to be Rh-positive. You’re Rh-negative only if both parents passed along the recessive version. This is why negative blood types are consistently rarer across every ABO group.
The A and B variants are ancient. The A/B split emerged at least 20 million years ago and has persisted across multiple primate species. The O allele, by contrast, arose from mutations that knocked out the gene’s function. There are actually several distinct O alleles in the human population, each representing a separate loss-of-function event at different points in our evolutionary history.
Blood Types Rarer Than AB-
Beyond the eight standard types, there are blood group systems so rare they affect only a handful of people on Earth. The rarest known is Rh-null, sometimes called “golden blood.” People with Rh-null blood lack all 61 antigens in the Rh system, not just the D antigen that defines standard Rh-negative. Only about 43 people have ever been identified with this blood type worldwide. Because Rh-null red blood cells can theoretically be given to anyone with rare Rh types, it’s extraordinarily valuable for transfusion, but finding a donor is nearly impossible.
The Bombay phenotype (also called Oh) is another extremely rare type. People with Bombay blood lack the foundational molecule that A, B, and O antigens are built on. Standard blood typing may misidentify them as type O, but they can only receive blood from other Bombay donors. Globally, the Bombay phenotype occurs in about 1 in 250,000 people. In India, it’s far more common: roughly 1 in 7,600 people, concentrated in southern and western states like Maharashtra, Karnataka, and Andhra Pradesh. In certain tribal populations in eastern India, the rate is dramatically higher, reaching as high as 1 in 33 in one community in Odisha. Consanguineous marriage, meaning marriage between close relatives, significantly increases the chance of inheriting this recessive trait.
Beyond ABO: The Kell System
Most people only think about A, B, AB, O, and Rh, but there are over 40 recognized blood group systems. The Kell system is the third most likely to trigger an immune response after ABO and Rh. About 1 in 10 people who are Kell-antigen-negative will develop antibodies if they receive Kell-positive blood, which can cause severe transfusion reactions.
The Kell-null phenotype, where red blood cells carry none of the Kell system antigens, occurs in roughly 0.001% of the population (with slightly higher rates in Finland and Japan). For patients who develop antibodies to common Kell antigens, finding compatible blood is extremely difficult because nearly everyone carries those antigens.
Why Rarity Matters for Donations
The practical impact of blood type rarity shows up in hospital blood banks every day. O-negative is the universal red blood cell donor type: it can be given to patients of any blood type in an emergency. That makes it the first blood pulled off the shelf in trauma situations, and it’s in constant demand despite making up only about 7% of the population. AB-positive, while the rarest common type, is the universal plasma donor, meaning AB plasma can go to any patient.
Shortages tend to hit hardest for O-negative and B-negative blood. These types are needed disproportionately to their availability. The American Red Cross consistently lists O-negative as one of the most needed types because it gets used faster than it’s donated. If you’re one of the roughly 1 in 15 people with O-negative blood, your donations carry outsized importance in emergency medicine.