O positive is the most common blood type in the world, carried by about 37% of the U.S. population alone. After that, the distribution drops off quickly, with some types shared by less than 1% of people. How common each blood type is depends on geography, ethnicity, and whether you’re counting the Rh factor (the “positive” or “negative” part).
Blood Type Distribution in the U.S.
The American Red Cross reports the following breakdown for the U.S. population: O positive leads at 37%, followed by A positive at around 36%, B positive at roughly 9%, AB positive at about 3%, O negative at 7%, A negative at 6%, B negative at about 2%, and AB negative at around 1%. That means roughly 80% of Americans carry one of just two blood types: O positive or A positive.
These numbers shift across ethnic groups. Type O blood is significantly more common among Latino donors (57%) and African American donors (51%) than among white donors (45%). This means blood banks serving diverse communities face different supply challenges than those in predominantly white areas, and it’s one reason organizations actively recruit donors from a range of backgrounds.
Blood Type Frequency in the UK
The picture looks slightly different in the United Kingdom, where NHS Blood and Transplant tracks donor statistics closely. O positive is still the most common at 36%, followed by A positive at 28%. B positive and O negative each account for about 8% and 14% respectively, while A negative sits at 8%, B negative at 3%, AB positive at 2%, and AB negative at just 1%. The higher proportion of O negative donors in the UK compared to the U.S. reflects the larger proportion of European ancestry in the British population, since Rh-negative blood is more common among people of European descent.
Why O Negative Gets Used So Quickly
O negative red blood cells can be given to anyone regardless of their blood type. That makes it the default choice in emergency rooms when there’s no time to test a patient’s blood. The result is a constant supply gap: only about 8% of donors are O negative, yet O negative accounts for roughly 13% of all hospital requests in the UK. Blood banks frequently issue targeted appeals to O negative donors to keep stocks from running dangerously low.
On the receiving end, AB positive is the universal recipient for red blood cells, meaning people with this type can accept transfusions from any donor. But AB positive is also the rarest of the common types, carried by only 2 to 3% of the population, so the advantage mostly benefits a small group.
The Rarest Blood Types in the World
Beyond the familiar eight types, there are hundreds of other blood group markers that can make someone’s blood exceptionally rare. The most extreme example is Rh-null, sometimes called “golden blood.” People with Rh-null lack all 61 antigens in the Rh blood group system, not just the D antigen that determines positive or negative status. Only about 43 people have ever been reported to have it worldwide. Their red blood cells can theoretically be given to anyone with a rare Rh blood type, but the supply is so limited that a single unit is extraordinarily precious.
Another rare type is the Bombay phenotype, in which a person’s red blood cells lack a precursor molecule that all standard blood types depend on. Someone with the Bombay phenotype tests as type O but can only receive blood from other Bombay-type donors. In India, where it was first discovered, it occurs in about 1 in 10,000 people. Among European populations, the rate drops to roughly 1 in 250,000 to 1 in 1,000,000.
Why Blood Types Vary by Region
The global distribution of blood types isn’t random. It was shaped over thousands of years by infectious disease. The clearest example involves malaria. Multiple studies have found that type O blood provides meaningful protection against severe malaria caused by the parasite Plasmodium falciparum. The mechanism involves a process called “rosetting,” where infected red blood cells clump together with uninfected ones. Type O cells resist this clumping more effectively, which reduces the severity of infection.
This is why type O is especially common in regions with a long history of malaria, including sub-Saharan Africa, Central America, and South America. Cholera has also played a role: research links blood type distribution in parts of South Asia to historical pressure from Vibrio cholerae. Over generations, people whose blood type offered even a slight survival advantage against the dominant local pathogen were more likely to pass their genes along, gradually shifting the blood type profile of entire populations.
What Your Blood Type Means for Donation
If you’re O positive, your blood is always in demand simply because so many patients share your type and need compatible transfusions. If you’re O negative, your donations are disproportionately valuable in emergencies. People with B negative blood (about 2 to 3% of the population) are among the hardest to find when a patient with that type needs a match. And if you’re AB positive, your plasma, rather than your red cells, is especially useful because AB plasma can be given to patients of any blood type.
Blood banks don’t just need more blood overall. They need the right mix, and that mix constantly shifts based on the patient population they serve. Hospitals in areas with large Latino or African American communities use more type O blood, while those in areas with large South Asian populations may need more type B. Knowing your blood type and donating regularly, especially if you carry a less common type, has an outsized impact on the people around you.