O positive is the most common blood type in the world, carried by roughly 39% of the global population. A positive comes in second at about 27%, followed by B positive at 22%. Together, these three types account for nearly nine out of every ten people on the planet.
All Eight Blood Types, Ranked by Frequency
Your blood type is determined by two systems working together: the ABO group (A, B, AB, or O) and the Rh factor (positive or negative). That creates eight common combinations. Here’s how they break down worldwide:
- O positive: 38.7%
- A positive: 27.4%
- B positive: 22.0%
- AB positive: 5.9%
- O negative: 2.6%
- A negative: 2.0%
- B negative: 1.1%
- AB negative: 0.4%
The pattern is clear: Rh-positive types dominate. Only about 6% of the world’s population is Rh-negative. That percentage shifts dramatically by region, though. In the UK, for example, around 14% of blood donors are O negative alone, compared to just 2.6% globally. Northern European populations carry much higher rates of Rh-negative blood than populations in Asia or Africa.
How Blood Type Varies by Region and Ethnicity
Global averages hide enormous geographic variation. Type O blood is especially common among Latino populations (about 57%) and African Americans (51%), compared to roughly 45% of white Americans. Type B is far more prevalent across South and Central Asia than in Western Europe or the Americas.
Beyond the basic eight types, there are over 300 known blood antigens, and some are unique to specific racial and ethnic groups. This is why blood banks actively recruit diverse donors. A patient who needs a rare antigen combination is most likely to find a match from a donor with a similar ethnic background. Matching on ABO and Rh alone is usually sufficient for a standard transfusion, but patients who receive frequent transfusions (such as those with sickle cell disease) often need closer matching across these additional antigen systems.
Why O Negative and AB Plasma Matter
O negative red blood cells can be given to patients of any blood type. That makes O negative the go-to choice in trauma situations when there’s no time to check a patient’s type. Since only about 7% of the U.S. population carries it, O negative supply is under constant pressure. Blood banks frequently issue urgent appeals specifically for this type.
O positive is in equally high demand for a different reason: sheer volume. It’s the most common type, so hospitals use more of it than any other. The American Red Cross identifies O positive as its most needed blood type.
The compatibility picture flips for plasma donations. AB plasma is the universal type for plasma transfusions, safe for recipients of any blood group. Since AB is the rarest ABO group (about 6% of the population combined), AB plasma donors are especially valuable even though AB red blood cell donations have a narrower recipient pool.
How You Inherit 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 you two copies. The A allele produces a specific molecule on the surface of your red blood cells. The B allele produces a different surface molecule. The O allele produces nothing functional at all.
A and B are both dominant over O, which means a person with one A allele and one O allele will have type A blood. Someone who inherits A from one parent and B from the other will have type AB, because both alleles are expressed equally. You need two copies of the O allele to have type O blood, which partly explains why O remains so common: the O allele is the most frequent version of the gene in most populations, even though it takes two copies to show up as type O.
The Rh factor follows a simpler pattern. Rh-positive is dominant, so you only need one copy of the Rh-positive allele to test positive. Two Rh-negative parents will always have Rh-negative children, but two Rh-positive parents can have an Rh-negative child if both carry one silent copy of the negative allele.
Blood Type and Disease Risk
A large genetic study published in eLife identified 49 diseases linked to ABO blood type. The strongest and most consistent connections involve blood clotting. People with type A or type B blood face a higher risk of cardiovascular disease and blood clots compared to those with type O. On the flip side, type O carriers are more prone to bleeding disorders.
These associations are real but modest. Having type A blood doesn’t mean you’ll develop heart disease any more than having type O guarantees you won’t. Standard risk factors like diet, exercise, smoking, and family history carry far more weight than blood type in predicting cardiovascular outcomes. Still, the clotting connection is consistent enough that researchers consider ABO type one of many small genetic variables that shape your overall risk profile.
Extremely Rare Blood Types
Beyond the familiar eight types, some people carry blood so rare it creates serious challenges for transfusion. The International Society of Blood Transfusion defines rare blood as lacking a common antigen found in more than 99.9% of people, or missing a combination of antigens that almost never occurs together.
Rh-null, sometimes called “golden blood,” lacks all Rh antigens entirely. Fewer than 50 people worldwide have been identified with it. The Bombay phenotype, which lacks a precursor molecule that all other blood types share, is another example. Some of these ultra-rare types have fewer than 10 registered donors on the planet. For people who carry them, finding compatible blood in an emergency can be a life-or-death logistics problem, which is why international rare donor registries exist to coordinate across borders.