O-positive is the most common blood type in the United States, carried by roughly 38% of the population. When you combine O-positive and O-negative, type O blood overall is found in about 45% of Caucasians, 51% of African Americans, and 57% of Hispanics, making it the dominant blood group across every major demographic in the country.
Full Breakdown of US Blood Types
There are eight main blood types, determined by two classification systems working together. The ABO system sorts blood by whether your red blood cells carry the A antigen, the B antigen, both, or neither. The Rh system then adds a “positive” or “negative” label based on whether a separate protein called RhD is present on the cell surface. Combine these two systems and you get eight types.
Here’s how they rank from most to least common in the general US population:
- O-positive: ~38%
- A-positive: ~34%
- B-positive: ~9%
- O-negative: ~7%
- A-negative: ~6%
- AB-positive: ~3%
- B-negative: ~2%
- AB-negative: ~1%
Together, O-positive and A-positive account for about 72% of the entire population. On the other end of the spectrum, AB-negative is the rarest type, found in roughly 1 in 100 people.
How Blood Type Varies by Ethnicity
Blood type frequencies shift noticeably across racial and ethnic groups. According to the American Red Cross, about 57% of Hispanic Americans carry some form of type O blood, compared to 51% of African Americans and 45% of Caucasians. Type B is more common among African American and Asian populations than among Caucasians, while type A tends to be more prevalent in people of European descent.
These differences matter for medicine. Certain rare blood subtypes are more common in specific ethnic groups, which means the donated blood supply needs to reflect the diversity of the patients who use it. For example, many patients with sickle cell disease require frequent transfusions, and the best match often comes from donors of African descent who share similar blood antigen profiles.
What Makes Blood Types Different
Your blood type comes down to what’s sitting on the surface of your red blood cells. Type A cells carry the A antigen, type B cells carry the B antigen, and type AB cells carry both. Type O cells carry neither, which is part of why O-type blood is so useful in emergencies.
The Rh factor works the same way. If your red blood cells have the RhD protein, you’re Rh-positive. If they don’t, you’re Rh-negative. About 85% of Americans are Rh-positive, which is why every positive blood type is more common than its negative counterpart. Your blood type is inherited from your parents and stays the same your entire life.
Why Compatibility Matters for Transfusions
When someone needs a blood transfusion, the donated blood has to be compatible with their own type. Give someone the wrong type and their immune system attacks the foreign blood cells, which can cause a life-threatening reaction. This is why hospitals type and crossmatch blood before a planned transfusion.
The basic compatibility rules work like this:
- Type O-negative can be given to anyone, regardless of their blood type. This makes it the universal red cell donor and the go-to choice in emergency rooms when there’s no time to check a patient’s type.
- Type AB-positive can receive red blood cells from all eight types, making it the universal recipient.
- Type O-positive can receive only from O-positive or O-negative donors.
- Type A can receive from type A and type O donors (matching Rh status).
- Type B can receive from type B and type O donors (matching Rh status).
If you have a common blood type like O-positive, finding compatible donors is straightforward. But you can only receive from other O donors, which limits your options compared to someone with type AB.
Which Types Are in Highest Demand
Being the most common doesn’t mean O-positive is always in surplus. Because so many people have it, hospitals burn through O-positive supplies faster than any other type. O-negative faces even more pressure: it makes up only about 7% of the population, yet it’s the only type safe for any patient in an emergency.
The American Red Cross has flagged types O, A-negative, and B-negative as particularly vulnerable during blood shortages. Negative blood types are always in shorter supply simply because fewer people have them, but demand stays constant because Rh-negative patients can only receive Rh-negative blood. During severe shortages, the Red Cross has reported the national blood supply dropping by as much as 35%, with these types hit hardest.
If you have O-negative, B-negative, or A-negative blood, your donations carry outsized impact. But every type is needed. Platelets, plasma, and whole blood all have to be stocked across the full range of types to keep hospitals running.
How to Find Out Your Blood Type
Many people don’t know their blood type unless they’ve donated blood, had surgery, or been pregnant. The easiest way to find out is to donate blood through the Red Cross or a local blood bank, which will type your blood and send you the results. Your doctor can also order a simple blood test. Some at-home kits use a finger prick and antigen cards to give you a result in minutes, though lab-confirmed results are more reliable.
Knowing your blood type is useful for medical emergencies, pregnancy planning (Rh incompatibility between a mother and baby can cause complications), and understanding your eligibility as a donor. If you’ve ever donated blood, that organization likely has your type on file.