How Can I Find My Blood Type?

Blood types were first classified at the beginning of the 20th century by Austrian scientist Karl Landsteiner. His work led to the identification of the main ABO blood groups, A, B, AB and O, and earned him the 1930 Nobel Prize in Physiology or Medicine.

Your blood type is determined by inherited characteristics of your red blood cells. Most people know their blood type as one of eight combinations, such as A positive, O negative or AB positive, but the science of blood groups is considerably more complex.

Contents

• Blood Type Basics
• How Can I Find My Blood Type?
• When Might My Blood Type Be Checked?
• What Is the Difference Between the Blood Types?
• Why Is It Important to Know My Blood Type?
• Can I Find My Blood Type with a Home Test?
• How to Use an EldonCard
• Conclusion

Blood Type Basics

The four main ABO blood groups are A, B, AB and O. Which group you belong to depends on the antigens found on the surface of your red blood cells and the antibodies present in your plasma.

Your blood type is also commonly described as positive or negative. This refers to the RhD antigen, one of the most important antigens in the Rh blood group system. If the D antigen is present, you are RhD positive. If it is absent, you are RhD negative.

This gives the eight blood types most people are familiar with:

• A positive
• A negative
• B positive
• B negative
• AB positive
• AB negative
• O positive
• O negative

These eight types do not represent the full complexity of human blood. As of 2026, the International Society of Blood Transfusion recognises 48 blood group systems and 397 red blood cell antigens. ABO and Rh remain particularly important when blood is being matched for transfusion.

You can find more information about recognised blood group systems in the International Society of Blood Transfusion Blood Group Database.

How common are the different blood types?

The proportions vary depending on whether figures refer to the general population or active blood donors. According to NHS Blood and Transplant data for donors, accurate at February 2026, the distribution is approximately:

• O positive: 36%
• O negative: 14%
• A positive: 28%
• A negative: 8%
• B positive: 8%
• B negative: 3%
• AB positive: 2%
• AB negative: 1%

O positive is the most common blood type among donors, while AB negative is the rarest of the eight main types. You can see the latest information on the NHS Blood and Transplant blood types page.

How Can I Find My Blood Type?

Many people do not know their blood type because it is not normally tested as part of routine GP care unless there is a medical reason for doing so.

If you do not know your blood type, there are several ways you may be able to find out. Your blood group may already be recorded if you have previously had certain medical investigations, been pregnant, received hospital treatment or donated blood.

When you donate blood, your donation is tested and you will be told your blood type. Alternatively, an ABO and RhD home blood group test can be used if you simply want to find out your blood group for your own information.

When Might My Blood Type Be Checked?

Healthcare professionals may need to establish your blood type in a number of circumstances. These can include:

• Before receiving a blood transfusion
• As part of preparation for certain operations or procedures
• When donating blood or blood products
• When donating an organ or preparing for some types of transplant
• During pregnancy

Blood-group testing is particularly important before a transfusion. Giving incompatible red blood cells can cause a potentially serious immune reaction, so hospitals use laboratory testing and compatibility checks before blood is given whenever circumstances allow.

Blood type during pregnancy

Pregnant women are offered blood-group testing during antenatal care. RhD status is important because complications can occur if an RhD-negative mother is carrying an RhD-positive baby and develops antibodies against the baby’s red blood cells.

If you are RhD negative, your maternity team will explain whether additional testing, monitoring or anti-D immunoglobulin is appropriate. You can read more about haemolytic disease of the fetus and newborn on the NHS website.

What Is the Difference Between the Blood Types?

The ABO blood group system is based mainly on whether A and B antigens are present on your red blood cells.

• Blood group A: red blood cells have A antigens.
• Blood group B: red blood cells have B antigens.
• Blood group AB: red blood cells have both A and B antigens.
• Blood group O: red blood cells have neither A nor B antigens.

Your plasma also contains antibodies that react against particular blood-group antigens. This is why ABO compatibility is so important when red blood cells are transfused.

The positive or negative part of your blood type usually refers to RhD. If the D antigen is present on your red blood cells, you are RhD positive. If it is absent, you are RhD negative.

Why Is It Important to Know My Blood Type?

Knowing your blood type can be interesting and useful, although you do not normally need to know it in advance of medical treatment. If you require a transfusion, healthcare professionals will carry out the necessary blood-group and compatibility testing rather than relying on a blood type reported by the patient.

O negative red blood cells are often described as the universal red-cell type because they can be given to people of any ABO or RhD group when necessary. This makes O negative blood particularly important in emergencies when there may not be enough time to establish a patient’s blood group.

AB positive patients, meanwhile, can receive compatible red blood cells from all eight main ABO and RhD blood types. Compatibility rules can differ for other blood components, such as plasma and platelets, so descriptions such as “universal donor” or “universal recipient” should always be understood in context.

Some research has investigated associations between particular ABO blood groups and the likelihood of developing certain health conditions. These associations do not mean that your blood type determines whether you will develop a disease. Many genetic, environmental and lifestyle factors influence individual health.

There is also no good evidence that people should choose particular foods or exercise programmes according to their ABO blood type.

Can I Find My Blood Type with a Home Blood Group Test?

Yes. A home blood group test can be used to determine the common ABO blood groups A, B, AB and O together with your Rhesus D status using a small finger-prick blood sample.

Zoom Health offers a Home Blood Group Test based on the EldonCard system. The card contains dried antibody reagents that react differently depending on the antigens present in your blood.

It is important to follow the instructions supplied with the test carefully. Unusual blood groups and rare subtypes cannot be identified using this type of home test and require specialist laboratory testing.

Important: A home blood group test should not be used to determine blood type for a blood transfusion. Hospitals carry out their own laboratory testing and compatibility procedures before transfusion.

How to Use the EldonCard Home Blood Type Test

An EldonCard provides a convenient way to determine your ABO and Rhesus D blood group at home using a small finger-prick blood sample.

The test kit contains the equipment needed to collect a small blood sample and apply it to the reagent areas of the card. Before beginning, read the instructions supplied with your particular kit from start to finish.

The test involves adding water to the reagent areas of the EldonCard, obtaining a finger-prick blood sample and transferring blood to the appropriate circles using the supplied applicators. The blood and reagents are then mixed as instructed and the card is tilted in different directions before the reaction pattern is compared with the result guide.

Different patterns of agglutination, where blood cells visibly clump together, indicate which ABO antigens and RhD antigen are present. This allows the card to identify your blood group.

Always use separate applicators for the different reagent areas and follow the timings and procedure in the instructions supplied with the test. If the result is unclear or cannot be interpreted confidently, do not guess your blood type.

How Can I Find My Blood Type? A Quick Summary

If you do not know your blood type, you may find it in existing medical records where blood-group testing has previously been necessary. You can also discover your type by donating blood or by using an appropriate home blood group test for personal information.

Your familiar A, B, AB or O blood group and positive or negative RhD status are only part of a much more complex blood-group system. For most people, however, these are the blood groups they are most likely to encounter in everyday healthcare.

A home blood group test can be a convenient way of satisfying your curiosity about your ABO and RhD type, but it is not a substitute for clinical blood-group testing. Blood used for transfusions is always matched using appropriate laboratory procedures.

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