How to find your blood type
What is my blood type? Five ways to find out, from free to fast, and how the test actually reads your blood.
Five ways to find out
- Donate blood. Free. Blood services type every donation and send you the result, often within a few days. Also helps someone else.
- Ask your doctor or check records. If you’ve had surgery, a transfusion, given birth or had pregnancy bloods, your type is likely on file. Some patient portals show it.
- Ask for a lab test. A doctor can order an ABO/Rh test. Some countries let you order one directly from a lab.
- Home test kit. Card kits (e.g. Eldon) use a finger-prick drop on dried antibodies. Results in minutes; accuracy depends on reading the card correctly.
- Consumer DNA test. Some DNA services predict ABO and Rh from your genes as a side result.
Your parents’ types narrow it down but can’t confirm it: see which types are possible with the blood type calculator.
Reading: A positive (A+). Anti-A and Anti-D clumped.
How to read a blood typing card
A typing card has wells coated with antibodies. Add a drop of blood to each and look for clumping (agglutination): grainy red specks on a clear background.
- Anti-A clumps → your cells carry A antigen (type A or AB).
- Anti-B clumps → your cells carry B antigen (type B or AB).
- Neither clumps → type O.
- Anti-D clumps → Rh positive; smooth → Rh negative.
- Control must stay smooth. If it clumps, the test is invalid.
Labs also do “reverse typing”, mixing your plasma with known A and B cells to confirm your antibodies match your antigens. That second check is what catches rarities like the Bombay phenotype.
Frequently asked questions
How can I find out my blood type for free?
Donate blood. Most blood services (the American Red Cross, NHS Blood and Transplant and others) test every donation and tell you your type afterwards, usually in their app or donor card.
Are at-home blood type tests accurate?
Card kits such as Eldon cards use the same antibody reagents as a lab and are generally reliable for ABO and Rh if you follow the instructions, but results can be hard to read, and weak variants may be missed. They are not accepted for medical purposes.
Is my blood type on my birth certificate?
Usually not. Some countries record it on medical cards or ID, but in the US and UK it is not on birth certificates. Your birth hospital or GP may have it if you were ever typed.
Can a DNA test tell me my blood type?
Some consumer DNA tests predict ABO and Rh from your genes. The prediction is usually right but not guaranteed; a serological test is the reference.
How does a blood type test work?
Drops of blood are mixed with anti-A, anti-B and anti-D antibodies. Wherever the antibody matches an antigen on your cells, the cells clump (agglutinate). The pattern of clumping gives your ABO and Rh type.