Knowing your blood type is important for things like blood transfusions, surgeries, pregnancy, and emergencies.
You have several options for finding out whether your blood type is A, B, AB, or O, and whether it’s postive or negative for rhesus factor (Rh factor), a type of protein on the cells’ surface that can affect your blood’s compatibility with someone else’s.
Your blood type may already be noted in your medical records if you have undergone blood tests, had surgeries, or done prenatal testing. You can ask your doctor if they have that information available, or check your previous lab test results. Hospitals also store your medical records, which you can access to know your blood type.
A doctor can order a blood test to have your blood typed. Blood typing is a procedure in which a healthcare provider draws a blood sample to send to a lab, where a lab technician can perform certain testing that reveals your blood type.
Blood donation centers type your blood as part of the processing. They do this so that when your blood is needed, doctors can ensure your blood type is compatible with the recipient’s. After you donate blood, you may receive a donor card that lists your blood type.
You can buy an at-home blood typing test kit to determine your blood type at home in a matter of minutes with a finger prick. These kits are available online, at pharmacies, or in some supermarkets. It’s important to use only FDA-approved or FDA-authorized tests.
About 80% of people secrete the antigens that tests use to determine blood type into their saliva. These people may be able to learn their blood type through a saliva test, which may be a good option if you have a fear of needles or blood.
Saliva tests may not accurately determine whether your blood type is positive or negative, however.
Your blood type depends on whether certain antigens are present on the surface of your red blood cells. Antigens are substances that can trigger an immune response if they are foreign to your body. The ABO system categorizes blood types as A, B, AB, and O based on the presence or absence of the A and B antigens:
- Type A: Has A antigens
- Type B: Has B antigens
- Type AB: Has both A and B antigens
- Type O: Has neither A nor B antigens
Each of the four main blood types may be positive (+) or negative (-) for Rh factor, making eight blood types.
Your blood type can affect whether you’re able to give or receive blood from people with different blood types. Most blood types are only compatible with the same blood type or an O-type blood.
O negative is known as the universal donor because it contains no antigen, so it doesn’t trigger an immune response even if the recipient has a different blood type. Just 7% of the population in the United States has this blood type, which is helpful in emergencies where the recipient’s blood type is unknown.
AB positive is known as the universal recipient, as it contains all the antigens and can receive blood from all blood types without complication. Less than 4% of the U.S. population has AB positive blood.
Rh factor is also an important consideration during pregnancy. If you have Rh negative blood but your developing fetus has Rh positive blood, your body may respond in negative ways. Treatments can help solve and prevent problems.
