O-positive is the most common blood type, found in about 37% of the U.S. population. A-positive comes in second. Together, these two types account for the majority of people, but the full picture involves eight main blood types that vary significantly by region and ethnicity.
The Eight Main Blood Types, Ranked
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 combination produces eight common blood types. In the U.S., their approximate frequency breaks down like this:
- O-positive: 37%
- A-positive: 36%
- B-positive: 8%
- O-negative: 7%
- A-negative: 6%
- AB-positive: 3%
- B-negative: 2%
- AB-negative: 1%
The numbers shift depending on the population. In the UK, O-negative is more common at around 14%, compared to 7% in the U.S. These differences reflect the genetic makeup of each country’s population rather than anything about geography itself.
What Makes a Blood Type Common or Rare
Blood type comes down to markers, called antigens, sitting on the surface of your red blood cells. Type A cells carry one kind of marker, type B cells carry a different one, and type AB cells carry both. Type O cells carry neither. Your immune system treats unfamiliar markers as threats, which is why mismatched transfusions can be dangerous: your body attacks the donated blood cells because it doesn’t recognize them.
The Rh factor adds another layer. If your red blood cells carry the Rh protein, you’re Rh-positive. If they don’t, you’re Rh-negative. Most people are Rh-positive, which is why all four positive blood types are more common than their negative counterparts.
Why Type O Is So Widespread
Everyone inherits two copies of the gene that determines ABO type, one from each parent. The A and B versions of this gene each code for an enzyme that builds a specific marker on red blood cells. The O version codes for a nonfunctional protein that builds no marker at all. Because you need two copies of the O version to actually have type O blood, you might expect it to be less common. But the O version is by far the most frequent allele in most human populations, so two-copy combinations happen often.
Type A is common for a similar reason: the A allele is the second most prevalent version of the gene worldwide. Type B and especially type AB are less common because the B allele occurs at lower frequencies in most populations, and AB requires inheriting one A allele and one B allele, a more specific combination.
How Blood Type Varies by Ethnicity
Blood type distribution is not the same across all groups. About 57% of Hispanic Americans are type O (positive or negative combined), compared to 51% of African Americans and 45% of white Americans. These patterns matter for blood banks. Because certain blood markers beyond the basic eight types are more common in specific ethnic groups, patients who need repeated transfusions often do best with blood donated by someone of a similar background. There are actually over 300 known blood antigens, and some are unique to particular racial and ethnic groups, making a diverse donor pool essential.
Universal Donors and Universal Recipients
O-negative holds a special role in medicine. Because O-negative red blood cells carry no A, B, or Rh markers, they won’t trigger an immune reaction in virtually any recipient. That makes O-negative the go-to choice in emergencies when there’s no time to test a patient’s blood type. Only about 7% of people are O-negative, though, which means blood banks face a constant shortage of this type.
On the other end, AB-positive individuals are sometimes called universal recipients. Their blood already contains both A and B markers plus the Rh protein, so their immune system won’t attack donated red blood cells of any common type. AB-positive is also the rarest of the eight main types, at roughly 3% of the population.
Beyond the Eight Common Types
The ABO and Rh systems are the most familiar, but they’re not the whole story. The Rh system alone involves dozens of different antigens. In extremely rare cases, a person can lack all Rh antigens entirely, a condition sometimes called “golden blood.” Fewer than 50 people in recorded medical history have ever been confirmed to have it. Golden blood can be donated to anyone who is Rh-negative regardless of their specific Rh profile, making it extraordinarily valuable, but its scarcity means people who have it face serious challenges if they ever need a transfusion themselves.
For most people, though, knowing your basic eight-type classification is what matters. It determines who you can safely receive blood from, who can receive yours, and whether certain precautions are needed during pregnancy if you’re Rh-negative and your baby is Rh-positive. Your blood type is identified with a simple test, and many people learn theirs the first time they donate blood.