There are several easy ways to find out your blood type, and most of them don’t require a special trip to a doctor’s office. If you’ve ever donated blood, had surgery, or been pregnant, there’s a good chance your blood type is already on file. If not, you can get tested through a quick lab draw or even an at-home kit.
Check Records You Already Have
Before ordering any test, look at what you might already have. If you’ve donated blood, your donor card or online donor portal will list your blood type. OneBlood, for example, posts your blood type to your donor portal within about 48 hours of your donation. The American Red Cross and other donation centers do the same.
If you’ve had a baby, your blood type was tested at your first prenatal visit. It’s part of routine early pregnancy bloodwork because Rh factor compatibility between mother and baby matters for the pregnancy. That result is in your medical record, and your OB’s office can pull it up with a phone call. The same goes for any past surgery requiring anesthesia: the hospital almost certainly typed your blood beforehand. Your primary care doctor’s office can usually access these older records through shared electronic systems.
Donate Blood
If you don’t have prior records and you’re eligible to donate, this is the most useful option. You find out your blood type for free, you get a basic health screening (cholesterol, blood pressure, iron levels), and someone else benefits from the donation. Most blood centers mail a donor card or update an online portal with your full ABO and Rh type within a few days.
Ask Your Doctor for a Blood Type Test
Any doctor’s office or lab can run a blood type test with a standard blood draw. The test itself is called ABO typing. A technician mixes a small sample of your blood with antibodies that react against type A and type B blood, then watches to see if the red blood cells clump together. If they clump when mixed with anti-A antibodies, you’re type A. If they clump with anti-B, you’re type B. If they clump with both, you’re AB. If neither causes clumping, you’re type O.
A second step called back typing confirms the result. The liquid portion of your blood (with the cells removed) is mixed with known A and B blood cells. Your natural antibodies will cause the opposite reaction, which serves as a double check. Rh typing works the same way, using antibodies against the Rh protein to determine whether you’re positive or negative. The whole process takes minutes in a lab, and results are typically available within a day or two.
Use an At-Home Blood Typing Kit
If you’d rather skip the doctor visit, at-home blood typing kits are widely available online for around $10 to $25. The most well-known is the EldonCard, which uses the same basic principle as a lab test: dried antibody reagents are embedded on a card, and you apply a drop of blood from a finger prick. Where the blood clumps, the corresponding antigen is present.
These kits are quite accurate when used correctly. A hospital comparison study found a kappa score of 0.932 between EldonCard results and standard lab tube testing, which represents excellent agreement. A larger multicenter study across Europe reported 99.9% concordance for ABO and Rh typing. The main source of error is user technique. You need to follow the instructions carefully, use enough blood, and read the results within the specified time window. That said, at-home results are not accepted for medical records. If you need your blood type documented for surgery or pregnancy, a lab test is still required.
The Eight Blood Types Explained
Your blood type is defined by two things: the ABO group and the Rh factor. Together, they produce eight possible combinations. The ABO group depends on which sugar molecules (antigens) sit on the surface of your red blood cells. Type A cells carry A antigens, type B carry B antigens, type AB carry both, and type O carry neither. Your immune system naturally produces antibodies against whichever antigens you lack, which is why mismatched transfusions are dangerous.
The Rh factor is a separate protein on the red blood cell surface. If you have it, you’re Rh-positive (written as a “+”). If you don’t, you’re Rh-negative (“-“). Combining these two systems gives you types like A+, O-, AB+, and so on.
In the U.S. population, the distribution is far from even:
- O+: 37.4% (the most common)
- A+: 35.7%
- B+: 8.5%
- AB+: 3.4%
- O-: 6.6%
- A-: 6.3%
- B-: 1.5%
- AB-: 0.6% (the rarest)
Nearly three out of four Americans are either O+ or A+. Meanwhile, fewer than 1 in 150 people are AB-.
Can You Guess From Your Parents’ Types?
If you know your parents’ blood types, you can narrow down the possibilities, though you usually can’t pinpoint your exact type without a test. The A and B genes are codominant, meaning if you inherit one of each, you’ll be type AB. The O gene is recessive, so you need two copies (one from each parent) to be type O. A parent who is type A could carry a hidden O gene (genotype AO), which means two type A parents can have a type O child.
Rh factor follows a similar pattern. Rh-positive is dominant, so you only need one copy of the Rh-positive gene to test positive. Two Rh-negative parents will always have Rh-negative children. But two Rh-positive parents can have an Rh-negative child if both carry a recessive negative gene. Parent blood types can rule out certain possibilities for a child, but they rarely narrow it down to a single answer.
Why Your Blood Type Matters
For most of daily life, your blood type is irrelevant. It becomes critical in a few specific situations. Before any planned blood transfusion, the hospital types your blood and cross-matches it against the donor unit to prevent a reaction. In emergencies where there’s no time for testing, hospitals default to type O red blood cells because they lack both A and B antigens and carry the lowest risk of triggering an immune response.
During pregnancy, Rh status is the key concern. If you’re Rh-negative and your baby is Rh-positive (inheriting the factor from the father), your immune system can develop antibodies against the baby’s blood cells. This is called Rh incompatibility. It rarely causes problems in a first pregnancy, but those antibodies can attack a future Rh-positive baby’s red blood cells. An antibody screening test during prenatal care detects whether this sensitization has occurred, and a preventive injection can stop it from happening.
Knowing your blood type ahead of time saves precious minutes in emergencies and helps you make informed decisions if you’re planning a pregnancy or want to become a targeted blood donor for a type in short supply.