Do you know your blood type? Many people don’t, and for the most part, that’s OK. In case of a blood loss emergency, though, it’s important for your doctors to know what kind of blood they can give you — and if they don’t know your blood type, they turn to Type O-negative blood, which is known as the “universal blood type.”
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
When your body is in need of a blood transfusion, the best blood type to receive is your own blood type. But in emergencies, Type O-negative blood — which only about 7% of individuals have — can be given to people of any blood type
“All blood donations are important, as they can be life-saving,” says emergency medicine physician Baruch Fertel, MD, “but donations of Type O-negative blood are especially vital.”
He explains what it means to be a universal blood donor and why it’s so critical to donate blood, especially if you’re Type O-negative.
What are blood types?
There are eight common blood types, and what type you have depends on whether or not your blood includes certain antigens, or substances that can make your immune system react. Your blood type is dependent on whether you have A and B antigens (from the ABO blood group), and the Rh(D) antigen (from the Rh blood group).
“They can also react with antibodies already formed,” adds clinical pathologist NurJehan Quraishy, MD. This means that if you were to receive a blood transfusion of a type of blood with different antigens than your own blood, your body’s immune system could start to attack itself, which can be deadly.
“Additionally, with the ABO blood group, you have pre-formed antibodies against the missing antigen on your red blood cells,” Dr. Quraishy says. “For example, a Type A individual has anti-B, and must not receive Type B blood.”
The four major blood types indicate whether you have A or B antigens — or both or neither.
- 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.
So, where do those plus and minus signs come in? Blood types can also be either negative or positive, depending on whether you have another antigen, the Rh(D) antigen. This is known as being Rh positive or Rh negative, though it’s usually just referred to as having a positive or negative blood type.
- If you have a positive blood type, you have the Rh(D) antigen. This is most common.
- If you have a negative blood type, you do not have the Rh(D) antigen. This is less common.
When you add all of these options together, it adds up to those eight common blood types.
How does blood donation work?
Donating blood is easy, relatively painless and life-saving. “Every two seconds, someone in the U.S. needs blood or platelets,” Dr. Quraishy says.
And if you have Type O-negative blood, your donation can help anyone in need, which is incredibly important. Here are some facts to know about Type O-negative blood and blood donations.
1. Almost anyone can receive Type O-negative blood
As the universal blood donor type, Type O-negative blood can go to almost anyone in need of blood. That makes it especially lifesaving in the case of time-sensitive emergencies where someone is losing a lot of blood.
“If we get a patient in the emergency department who has sustained a major injury and is bleeding, time is of the essence, and we don’t always have time to figure out their blood type,” Dr. Fertel explains. “In that case, we give them Type O-negative blood.”
“It’s a very important blood type and one we certainly need in abundance,” he adds.
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.
3. Positive blood types can receive Type O-positive blood
While not as universal as Type O-negative blood, donations of Type O-positive blood are also in high demand. Type O-positive blood can be given to anyone with a positive type: other people with Type O-positive, as well as people with Types A-positive, B-positive and AB-positive blood.
4. One super-rare blood type can’t receive Type O-negative blood
Rare blood types occur in 0.1% or less of people. Having a rare blood type means your blood lacks an antigen most people have or that it has an antigen most people lack. The vast majority of people with rare blood types can still receive Type O-negative blood.
The exception is people with “golden blood.” An estimated 1 in 6 million people have this very rare type, technically known as Rh null blood, as it lacks all Rh antigens, not just D. There are fewer than 50 people on the planet who are known to have it, and they can’t receive Type O-negative blood — only other Rh null blood.
Who can donate blood?
“When it comes to blood donations, everything counts,” Dr. Fertel says. “Any blood that can be given in a blood transfusion can really make a difference in saving someone’s life.”
People of all blood types are welcomed and encouraged to donate, so long as they meet eligibility requirements. You can donate whole blood every 56 days, so long as you:
- Are generally in good health.
- Are at least 17 years old, in most states (or 16 years old with parental consent, in others).
- Weigh at least 110 pounds (though additional height and weight requirements apply for teenage donors).
Some restrictions apply, so check out the American Red Cross’s full list of eligibility requirements for donating blood before you head to a local donor drive.
What happens when you donate blood?
Once you begin the process, donating blood is simple.
“A trained professional will insert a brand new, sterile needle in your arm to extract some of your blood,” Dr. Fertel explains. “After that blood has been tested, it goes through various preservation mechanisms and is divided up to give to people who need it.”
How to learn your blood type
For the most part, Dr. Fertel says it’s helpful but actually not critical to know your own blood type. “Hospitals have to verify your blood type every time you’re in need, even if you already know it,” he notes. “Before giving you blood, they have to make sure it’s safe and effective — which is why O-negative can be helpful in time-sensitive emergencies.”
Still, there are a few ways to learn what your blood type is.
- Through your medical records: If you’ve had blood drawn for an operation or pregnancy, your doctor’s office should have a record of your blood type. And if your doctor’s office uses an online medical recording system such as MyChart, you can find that information in your account.
- Through a blood donation center, for example, the American Red Cross: When you donate blood, the donor card you receive afterward lists your blood type, as does your account in the organization’s app.
Regardless of your blood type, if you’re eligible, consider donating. It’s a simple, relatively painless and lifesaving way to help others in need. “Any blood type is helpful,” Dr. Fertel reiterates. “Any blood type can make a difference in somebody’s life.”