O positive is the most common blood type. It accounts for about 37.4% of the U.S. population, and it holds the top spot in nearly every major ethnic and geographic group worldwide. A positive comes in a close second at 35.7%, meaning these two types alone cover nearly three-quarters of the population.
Full Breakdown of Blood Type Frequency
There are eight main blood types, determined by two systems: the ABO group (A, B, AB, or O) and the Rh factor (positive or negative). Here’s how they break down in the U.S. population:
- O positive: 37.4%
- A positive: 35.7%
- B positive: 8.5%
- O negative: 6.6%
- A negative: 6.3%
- AB positive: 3.4%
- B negative: 1.5%
- AB negative: 0.6%
Rh-positive types are far more common overall. About 85% of people are Rh positive, which is why the negative versions of every blood type appear in much smaller numbers.
How Blood Type Varies by Ethnicity
O positive leads across all major ethnic groups, but the margins shift considerably. According to American Red Cross data, 53% of Latin Americans are O positive, compared to 47% of African Americans, 39% of Asian Americans, and 37% of Caucasians. That makes O positive especially dominant in Latin American populations.
Type B positive shows the reverse pattern. It’s relatively uncommon in Caucasian and Latin American populations (about 9% each) but reaches 25% in Asian Americans and 18% in African Americans. These differences reflect the genetic history of different populations, since blood type is inherited and certain alleles became more or less frequent as groups migrated and evolved in relative isolation.
The rarest common types also shift by group. AB negative is the least common type across the board, but it’s vanishingly rare in Asian Americans (0.1%) compared to Caucasians (1%).
What Determines Your Blood Type
Your blood type comes down to what’s sitting on the surface of your red blood cells. People with type A blood have A markers (antigens) on their cells. Type B has B markers. Type AB has both, and type O has neither. The Rh factor adds one more marker: if you have the RhD protein on your cells, you’re positive. If not, you’re negative.
You inherit one allele from each parent, and the combination determines your type. The A and B alleles are codominant, meaning if you get one of each, both markers show up and your blood type is AB. The O allele is recessive. It codes for a nonfunctional protein that doesn’t produce any surface marker at all. So to actually have type O blood, you need to inherit the O allele from both parents. Someone with type A blood could carry either two A alleles or one A and one O, since the A allele masks the O.
This inheritance pattern is why two parents with type A blood can have a child with type O. If both parents carry a hidden O allele, there’s a one-in-four chance their child inherits both copies and ends up with type O.
Why Blood Type Matters for Transfusions
Your immune system produces antibodies against the blood markers you don’t have. If you’re type A, your plasma contains anti-B antibodies. If you receive type B blood, those antibodies attack the transfused cells, which can trigger a life-threatening reaction. This is why matching blood types is critical.
O negative is the universal red cell donor type. Because O negative cells carry no A, B, or RhD markers, there’s nothing for the recipient’s immune system to attack. In emergencies where a patient’s blood type is unknown, O negative is what gets used. On the other end, AB positive is the universal recipient for red cells, since people with AB positive blood have no antibodies against A, B, or RhD markers.
This creates a supply problem. Only about 6.6% of the population is O negative, but O negative makes up roughly 13% of hospital requests, according to NHS Blood and Transplant data. The gap between supply and demand for O negative is a persistent challenge for blood banks.
The Rarest Blood Type in the World
AB negative is the rarest of the eight standard types, found in just 0.6% of the U.S. population. But there are blood types far rarer than that.
The rarest known type is Rh-null, sometimes called “golden blood.” People with Rh-null blood lack all Rh system proteins, not just the D protein that makes someone Rh negative. Fewer than 50 people in recorded history have ever been identified with it. Because Rh-null red cells can be transfused to anyone with a rare Rh blood type, each donor is extraordinarily valuable, which is how it earned its nickname.
Beyond Rh-null, there are dozens of other rare subtypes tied to specific ethnic populations. The Ro subtype, for example, is most common in people of African descent but only 2% of regular blood donors in England carry it, creating chronic shortages for patients who need it.