What Does It Mean To Be a Universal Blood Donor?

If you need a blood transfusion, your doctors will check your blood type so they know what kind of blood they can give you.

The best blood type to receive is your own. But in an emergency, type O negative (or O-) red blood cells can be given to people of any blood type. That’s why it’s known as the “universal blood type” — and only about 7% of people have it.

What makes O negative the universal red blood cell?

Though people often call O negative the universal blood type, it’s more specifically the universal red blood cell donor type. In an emergency, O negative red blood cells can be given to almost anyone because they don’t have certain markers (antigens) that can trigger a harmful immune response.

“Not all blood types are compatible with one another, so in a blood loss emergency, you can only receive specific types of blood,” explains family medicine physician Charles Garven, MD. “But type O negative blood is compatible with every other blood type, except in very rare circumstances.”

Blood types are based on whether your red blood cells have certain antigens. The main antigens are called A, B and Rh(D).

• Type A blood has the A antigen.
• Type B blood has the B antigen.
• Type AB blood has both A and B antigens.
• Type O blood has neither A nor B antigens.

Blood is also either positive or negative:

• Positive blood has the Rh(D) antigen.
• Negative blood does not have the Rh(D) antigen.

When you add all of these options together, it results in those eight common blood types — and O negative blood is the one type that doesn’t have any of these antigens.

“If you receive a blood transfusion with antigens that don’t match your blood type, your immune system may attack the transfused blood cells, which can be life-threatening,” Dr. Garven says. “Because O negative red blood cells don’t have A, B or Rh(D) antigens, they’re less likely to trigger an immune response.”

What else to know about type O- blood

There’s more to know about type O negative blood. Here are some interesting (and important!) facts about this critical but relatively uncommon blood type.

1. It’s especially important in blood-loss emergencies

“In an emergency where someone is losing a lot of blood, time is of the essence,” Dr. Garven states. “There’s not always time for emergency department staff to figure out a patient’s blood type.”

In those cases, they’re given type O negative blood, making it especially critical to have on hand.

2. People with type O negative blood can only receive type O negative blood

If you have type O negative blood, you can give blood to anyone. But you can only receive blood from other people who also have type O negative blood.

“Because your blood doesn’t have A, B or Rh(D) antigens, your immune system would react to the antigens found in other blood types,” Dr. Garven explains.

3. One super-rare blood type can’t receive type O negative blood

Having a rare blood type means your blood lacks an antigen most people have or that it has an antigen most people lack. Rare blood types occur in 0.1% or less of people — and the majority of these people can still receive type O negative blood.

The exception is people with Rh null blood, aka “golden blood,” which lacks all Rh antigens. An estimated 1 in 6 million people have this very rare type, and they can’t receive type O negative blood — only other Rh null blood.

4. Type O positive blood isn’t quite as universal as type O negative blood

Donations of type O positive blood are also in high demand, as they can be given to anyone with a positive type: other people with type O positive, as well as people with A positive, B positive and AB positive blood types.

“All blood donations are important, as they can be lifesaving,” Dr. Garven states. “But donations of type O blood are especially vital.”

Other universal donors

Red blood cells aren’t the only blood component that can be donated and transfused to people in need. Plasma and platelets can be, too — but type O negative is not the universal donor for these two components.

• Plasma helps blood flow like liquid, and it carries vital proteins and chemical compounds through the body. People of any blood type can receive AB plasma, which is why the American Red Cross calls type AB plasma donation “AB Elite.”
• Platelets help blood clot. Though platelet matching is more nuanced than red blood cell and plasma matching, type AB negative is typically considered universal.

A blood donation center (like the American Red Cross) can guide you toward the type of donation that can help the most people, based on your blood type.

“People with type O negative blood are typically encouraged to donate red blood cells rather than plasma or platelets,” Dr. Garven clarifies. “On the other hand, people with type AB positive blood are encouraged to donate plasma and platelets.”

Final thoughts

Regardless of your blood type, consider donating if you’re eligible.

Don’t know your blood type? The best way to find out is through donation or if you’ve donated in the past. It’s rarely listed in your medical records. But the donation center will take care of everything — and after you’ve donated once, you’ll know for the future.

“Giving blood is a simple, relatively painless and lifesaving way to help others in need,” Dr. Garven encourages. “Any blood type is helpful. And any blood type can make a difference in somebody’s life.”