Blood group and Rh typing
Note: this site is for informational purposes only. To view test results or book a test, use the NHS app in England or contact your GP.
Blood group and Rh typing tests find out your blood group (A, B, AB or O) and whether you have the RhD factor (positive or negative). Knowing this is essential before a blood transfusion or organ transplant and is routinely tested during pregnancy to keep you and your baby safe.
Who needs this test
You will need a blood group and Rh typing test if:
- you need a blood transfusion — your blood must be matched to the donated blood to prevent a serious reaction
- you are donating blood — the donation centre needs to know your blood type so it can be given safely to the right recipients
- you are pregnant — all pregnant women are tested to check whether they are RhD negative, which can affect your care and your baby’s wellbeing
- you are having major surgery where a blood transfusion may be needed
- you have a condition such as severe anaemia, sickle cell disease, thalassaemia, a bleeding disorder, or cancer where regular transfusions are needed
- you are having an organ or stem cell transplant
Newborns of RhD-negative mothers are also tested after delivery to help determine whether the mother needs a preventive injection (anti‑D immunoglobulin).
Preparing for your test
You do not need to do anything to prepare for this test. A small blood sample is taken from a vein in your arm. For newborns, blood from the umbilical cord or a heel prick may be used. In some situations, a finger-prick sample is sufficient.
Understanding your results
What the test measures
Your red blood cells have proteins on their surface called antigens. The combination of antigens you have determines your blood group. If you receive blood containing antigens that your body does not recognise, your immune system may attack the donated red blood cells. This is called a transfusion reaction and can be life-threatening. Blood typing prevents this from happening.
The test looks at two blood group systems.
The ABO system
The ABO system divides blood into four groups based on whether your red blood cells carry the A antigen, the B antigen, both, or neither:
- Group A – you have A antigens on your red blood cells and anti‑B antibodies in your blood plasma
- Group B – you have B antigens on your red blood cells and anti‑A antibodies in your blood plasma
- Group AB – you have both A and B antigens, and no ABO antibodies. Patients who are AB are described as ‘universal recipients’ for red blood cells.
- Group O – you have no A or B antigens, but you have both anti‑A and anti‑B antibodies. Group O patients are ‘universal donors’ for ABO blood groups.
The RhD system
The RhD system checks the second most important blood group. There are several antigens in this blood group, the most important of which is RhD. If this antigen is present on your red blood cells, you are RhD positive. If it is absent, you are RhD negative. Your ABO group and RhD type are combined to give your full blood type — for example A positive or O negative.
Unlike ABO antibodies, RhD antibodies do not develop naturally. They only form if an RhD-negative person is exposed to RhD-positive blood — through a transfusion, pregnancy, or organ transplant. This exposure is called sensitisation. After sensitisation, future exposure to RhD-positive blood can cause a serious immune reaction.
What your results mean
Your result tells you your ABO group and whether you are RhD positive or negative. It also determines which blood types you can safely receive.
The table below shows which blood types each group can receive:
| Your blood type | You can safely receive |
|---|---|
| A positive | A positive, A negative, O positive, O negative |
| A negative | A negative, O negative |
| B positive | B positive, B negative, O positive, O negative |
| B negative | B negative, O negative |
| AB positive | Any ABO / RhD blood type (universal recipient) |
| AB negative | AB negative, A negative, B negative, O negative |
| O positive | O positive, O negative |
| O negative | O negative only (but universal donor for others) |
O negative blood can be given to anyone in an emergency, because it has no A, B or RhD antigens. This is why it is used when there is no time to test a patient’s blood group — for example in a major accident or emergency surgery. Stocks of O negative blood are limited, so hospitals try to reserve it for emergencies.
O RhD positive blood may be given in an emergency to patients who will not become pregnant in the future. Many hospitals therefore give O RhD positive blood to male adults and female adults aged 51 and over.
Blood group distribution in the UK
Blood groups are inherited from your parents and do not change throughout your life. The approximate distribution of blood groups in the UK is:
| Blood type | RhD positive | RhD negative | Total |
|---|---|---|---|
| O | 37% | 7% | 44% |
| A | 35% | 7% | 42% |
| B | 8% | 2% | 10% |
| AB | 3% | 1% | 4% |
If you are RhD negative and pregnant
If you are RhD negative and your baby’s father is RhD positive, your baby may inherit the RhD antigen. During pregnancy or at delivery, a small amount of your baby’s blood can enter your bloodstream. Your immune system may then produce antibodies against the RhD antigen — a process called sensitisation.
If you become sensitised and have another RhD-positive pregnancy, these antibodies can cross the placenta and attack your baby’s red blood cells. This is called haemolytic disease of the fetus and newborn (HDFN) and can cause serious illness or, in severe cases, be life-threatening for the baby.
To prevent this, you will be offered an injection of anti‑D immunoglobulin during pregnancy and again after delivery if your baby is RhD positive. This treatment is safe and very effective. Your midwife or doctor will explain when and how it is given.
Questions to ask your doctor or midwife
What happens next
If you need a blood transfusion, the laboratory will use your blood group result to find a compatible unit of blood. For planned surgery or treatment, blood can be matched in advance. In emergencies, O negative blood can be given straight away while typing is carried out.
If you are pregnant and RhD negative, your maternity team will arrange anti‑D immunoglobulin injections as part of your routine care. These are given at set times in pregnancy and after delivery if needed.
If you are donating blood, your blood type will be recorded so that donated units can be matched appropriately to patients in need.
Your blood group does not change over time. Once typed, the result is recorded in your medical records and can be used for future transfusions. However, hospitals routinely re-test before any transfusion as a safety check.
What can affect your results
Blood group and Rh typing are very reliable tests. In rare cases, results may be affected by:
- recent blood transfusions — donated cells in your blood can temporarily affect grouping results
- certain diseases affecting the immune system or bone marrow, which may alter how antigens are expressed
- rare inherited conditions that cause weak expression of blood group antigens
- laboratory errors (very rare) — this is why hospitals confirm your blood group using at least two separate samples before a transfusion
Other tests you might need
Blood group and Rh typing is often part of a broader set of compatibility checks before transfusion. These may include:
- Antibody screen (indirect antiglobulin test) – checks whether you have developed any unexpected antibodies against other blood group antigens, beyond the routine ABO and RhD ones
- Crossmatch – directly tests your blood against a specific unit of donor blood before transfusion to confirm compatibility
- RBC antibody identification – if an unexpected antibody is found, this test identifies exactly which antigen it targets
- Direct antiglobulin test – checks whether antibodies are already attached to your red blood cells, which can happen in HDFN or certain types of anaemia
About blood groups
Blood groups are inherited characteristics determined by the antigens on your red blood cells. The ABO and RhD systems are the most clinically important, but there are over 40 other recognised blood group systems. Knowing your blood group is important for safe transfusion and certain aspects of maternity care.