What Are Blood Types?
While everyone’s blood contains the same basic parts, there are eight different blood types. The type you have depends on genes you inherit from your biological parents.
What makes your blood different from someone else’s is your unique combination of protein molecules, called antigens and antibodies. Antigens live on the surface of your red blood cells. Antibodies are in your plasma. Your blood type is based on the combination of antigens and antibodies in your blood.
“Every person has a combination of proteins or antigens on their red blood cells. These proteins are what make up someone’s blood type,” says Lauren Merz, MD, a hematology fellow at Dana-Farber Cancer Institute and Mass General Brigham in Boston. “The presence or absence of these proteins is inherited from each parent. This means blood types can run in the family and certain blood types are more common in certain communities.”
Blood basics
Most people have about 4 to 6 liters of blood in their body. Your blood is made up of different kinds of cells that float in plasma, a fluid made up of salts and proteins. The different cell types in your blood include:
- Red blood cells, which deliver oxygen to tissues and remove carbon dioxide
- White blood cells, which destroy invaders and fight infection
- Platelets, which help your blood clot
Different Blood Types
Multiple blood types exist, and some are only compatible with specific types.
Eight of the most common blood types include:
A positive. This is one of the most common blood types, with 35.7% of the U.S. population having this type). If you have this type, you can give blood only to people who are A positive or AB positive.
A negative. If you have this rare blood type (like 6.3% of the U.S. population), you can donate blood to anyone with A or AB blood type.
B positive. Another rare type, it is found in 8.5% of people. It is compatible only with B positive or AB positive blood.
B negative. Someone with this very rare blood type can give blood to anyone with B or AB blood type. Only about 1.5% of Americans are B negative.
AB positive. If you have this rare blood type (found in 3.4% of Americans), you can receive blood or plasma of any type. You’re known as a universal recipient.
AB negative. This is the rarest blood type, with only 0.6% of the U.S. population having it. If you have this blood type, you’re called a “universal plasma donor,” because anyone can receive this type of plasma.
O positive. This is one of the most common blood types, found in 37.4% of people. O-positive donors can give blood to anyone with a positive blood type.
O negative. If you have this rare blood type like 6.6% of Americans, you can donate it to anyone with any blood type.
The four major blood groups are based on whether or not you have two specific antigens — A and B. Doctors call this the ABO Blood Group System.
- Group A has the A antigen and B antibody.
- Group B has the B antigen and the A antibody.
- Group AB has both A and B antigens but neither A nor B antibodies.
- Group O doesn’t have either A or B antigens but has both A and B antibodies.
The third kind of antigen is called the Rh factor. You either have this antigen (meaning your blood type is “Rh+” or “positive”), or you don’t (meaning your blood type is “Rh−” or “negative”). In other words, the “positive” or “negative” next to blood type refers to the presence or absence of the Rh factor on your red blood cells.
Rare Blood Types
Researchers know a lot about major blood types like A, B, AB, and O, Merz says. They’re learning more about less common, or rare, blood types.
In fact, some blood types are only found in people who have the same race or ethnicity. For example, many people who self-identify as Black, African American, Middle Eastern, or Northern African in the U.S. will have the Duffy null blood type. “This is a normal and healthy blood type,” Merz adds.
Rare types of blood such as U-negative and Duffy-negative (or Duffy null) are common in people in Africa or the Arabian Peninsula — areas where malaria is common. Duffy null blood type can protect people from malaria, as malaria parasites use the Duffy protein to enter the red blood cells and cause infection, Merz explains.
Duffy null does result in a lower number of infection-fighting cells known as neutrophils. That may sound like someone with the blood type is more at risk for infection or disease, but that’s not true, Merz says. It just means that doctors need to check if neutrophil counts represent health or disease, she says.
Challenges of rare blood types
While it can be hard to get donations of all blood types, ensuring an ample supply for people with rare blood types is even harder. In some cases, the donor must be a certain race or ethnicity to be a match.
Before a transfusion, the blood is matched to make sure the donor’s blood is compatible with the recipient’s blood. That’s why having a diverse range of donors is a must to ensure all blood types are available.
The American Red Cross launched its Sickle Cell Initiative because blood donors who are Black are almost three times more likely to match the blood type most needed by individuals with sickle cell disease.
Nationwide, only 12% of blood donations come from donors of diverse backgrounds — despite the fact that nearly 40% of the U.S. population doesn’t identify as White, the organization reports.
Blood Type Importance
Blood groups were discovered in 1901 by an Austrian scientist named Karl Landsteiner. Before that, doctors thought all blood was the same, so many people died from blood transfusions.
Now experts know that if you mix blood from two people with different blood types, the blood can clump, which may be fatal. That’s because the person receiving the blood has antibodies that will actually fight the cells of the donor blood, causing a toxic reaction.
For a blood transfusion to be safe and effective, the donor and recipient need to have blood types that are compatible. People with blood group A can safely get group A blood, and people with blood group B can receive group B blood.
It’s best when a donor and recipient are an exact match and their blood goes through a process called crossmatching. But the donor doesn’t always need to have the exact same blood type as the person receiving it. Their types just have to be compatible.
Best Blood Types to Donate
If you’re thinking about donating blood, check with your local blood bank to confirm that you can give blood. Blood banks need all types of blood, especially because some people have the rarest blood types. Depending on the part of the blood, donations only last a certain amount of time. This is why regular donors are critical.
Blood type compatibility
If you need a transfusion, your clinical team will check which type of blood is compatible with yours to avoid an immune reaction.
For example, if you have type A blood, you will only be able to receive type A or type O blood. If you have type B blood, you can only receive type B or type O blood. You can receive any type of blood if you have type AB blood, but you can only receive type O blood if you have type O blood.
Universal donor blood type
Type O negative is often called the universal donor blood type because it can be transfused, or given, to anyone. That’s because type O-negative blood cells don’t have antibodies to A, B, or Rh antigens. Type O-negative blood is usually given in a life-threatening emergency when there’s no time to match blood, or when there’s a limited supply of the ideal blood type. Transfusing it can still carry risks.
If you have type O negative or positive, the blood bank may request your whole blood or just red blood cells. Donors with other types of blood may be commonly asked to donate platelets because they help blood clot, which is beneficial in treating people with blood cancers.
Universal recipient blood type
If you have AB-positive blood — known as the universal recipient blood type — you can receive red blood cells from people with all types of blood.
The chart below gives an overview of blood type compatibility between donors and recipients.
Blood Type Chart
| Blood Type | Who Can Receive This Type |
|---|---|
| O+ | O+, A+, B+, AB+ |
| O- | All blood types |
| A+ | A+, B+ |
| A- | A+, A-, AB+, AB- |
| B+ | B+, AB+ |
| B- | B+, B-, AB+, AB- |
| AB+ | AB+ |
| AB- | AB+, AB1 |
Blood Type Test
If you donate blood, the health care provider will want to make sure that your blood type is the right match for a recipient. Likewise, if you need a transfusion, they will make sure that the blood you receive is compatible with yours.
Labs use a method called blood typing to find out your blood type. The lab technician will run an ABO typing test on your blood by mixing your blood with antibodies against type A and B blood. If your blood reacts and cells stick together, it indicates a match with one of the antibodies, determining your blood type.
The technician can also use a process called back typing to check your blood type. For this test, the worker will mix your blood serum, or liquid part of your blood without cells, with blood that’s either type A or type B. People with type A blood show anti-B antibodies, and vice versa. (Type O has both kinds of antibodies).
Once the lab knows your blood type, they can select a donor blood that’s compatible with yours. Then, they’ll do a crossmatch to make sure it’s the perfect fit.
If you’re a blood donor, check out the report you receive after donating, because it will include your blood type.
Blood Type and Your Health
Your blood type may mean that you’re more at risk for certain conditions or diseases, but it isn’t the only factor that goes into your risk. Most research shows a link between blood type and diseases, but it doesn't mean that having a certain blood type will definitely cause a disease.
One blood type isn’t healthier than another, Merz notes.
“Blood types are like eye color or height — something you inherit from your parents that adds to the unique variation we see across humanity. Just like eye color or height, there are no blood types that are better or worse than others. They are just different,” Merz says.
Merz points out that some blood types are linked to differences in how other blood work is interpreted by doctors, though. For example, if you have the Duffy null blood type, you have fewer neutrophils in your bloodstream than those with the Duffy non-null blood type.
“Knowing your blood type can help health care workers give you the best possible advice about your medical care and make sure that you are able to enroll in clinical trials and receive important medications if you need them,” Merz adds.
Blood Type Diet
Over the past decade, there have been many claims about a “blood type diet,” in which you eat specific foods for your blood type to lower your risk of certain diseases and improve your overall health. There’s a lack of scientific evidence that eating for your blood type makes you any healthier, but no solid proof that a blood type diet is harmful, either.
Blood Type and Pregnancy
When you're pregnant, the fetus will get its Rh factor from either of its parents. But if you are Rh-negative and your fetus ends up with Rh-positive blood, that can cause complications for you and your pregnancy. So, very early in your pregnancy, your doctor will find out your blood type and screen you for antibodies. This is to check if your blood’s antibodies will attack your fetus’ blood cells (if you have Rh-negative blood and the fetus has Rh-positive blood, for instance).
If this is the case, your doctor will give you Rh immunoglobulin (RhIg) to block your antibodies from fighting the fetus’ blood.
Takeaways
Your blood type — whether a common or rare type — is passed down from your biological parents. It’s a good idea to know your blood type for your own health, especially if you need a transfusion in the future. It’s also important to know what type of blood you carry if you choose to donate blood.
Blood Type FAQs
What is the most common blood type?
The most common blood type is O positive, and about 37% of the population has it.
What is the rarest blood type?
The most rare type of blood is Rh-null. Less than 50 people in the world have this blood type, which is also called golden blood. Other rare types of blood include Duffy, K antigen (or Kell), Lutheran, and Kidd.
What's the healthiest blood type?
There is no healthiest blood type; all types of blood are healthy.
What blood type lives the longest?
Research is mixed on this, and much of it has shown loose links between blood type and how long a person will live. Some studies suggest those with B and AB live shorter, while those with type O may live longer.
Which is the most unhealthy blood group?
Some types of blood are linked to different conditions and diseases. For example, those with type A, B, or AB blood may have a higher risk for heart attacks. But your blood type isn’t the only factor that leads to a health ailment.
What is so special about O-negative blood?
O-negative blood is the universal blood type, which means that it is compatible with every blood type. It’s the most common type used during trauma and emergency cases where the blood type of the person isn’t known. However, a person with O-negative blood can only receive O-negative blood.