Why a full blood count is done
A full blood count measures the number, size and types of cells in your blood (such as red blood cells and white blood cells).
It can help check for or monitor many different conditions.
Reasons it may be done include to:
- diagnose or monitor conditions such as anaemia (where you have a low level of red blood cells or your red blood cells are unable to carry as much oxygen as normal)
- check if you might have an infection
- monitor a treatment you're having (some medicines and cancer treatments can affect your blood cells)
- check your general health or check if you're well enough to have surgery (alongside other tests)
How a full blood count is done
You do not need to do anything to prepare for a full blood count test. You can eat and drink as normal.
During the test:
- a healthcare professional will take a small amount of blood, usually from the inside of your elbow, using a needle
- a tight strap (tourniquet) will be put around your arm first – this helps to make taking blood easier
- you'll feel a scratch as the needle goes in, which may be a bit uncomfortable
- your blood will be collected in a small tube which will be sent to a lab for testing
After the test, you'll usually be given some cotton wool or a plaster to cover the area where the blood was taken.
You may get some bruising or swelling around the area where your blood was taken, but this should go away after a few days.
Getting your full blood count results
You'll usually get the results of a full blood count test after a few days.
A healthcare professional may contact you to discuss your results and explain what happens next.
You may not always be contacted if the healthcare professional is not concerned about your result and does not think you need any more tests or treatment.
If you want to know your result and do not hear anything after a few weeks, contact the GP surgery or specialist who arranged the test.
View your results online
You may be able to see your test results using the NHS App or by logging into your account on the NHS website.
Understanding your full blood count results
A full blood count includes several tests to check your:
- red blood cells and haemoglobin – these carry oxygen around your body
- white blood cells – these help your body fight infections
- platelets – these help your blood to clot when you're bleeding
Your results will be checked against results that doctors consider to be normal for most healthy people. This is called the "reference range".
If a result is lower or higher than this range, it does not always mean there's a problem. What's normal can vary for different people and can depend on your age, sex and ethnicity.
Some results can also be affected by things like dehydration, stress, smoking, a recent illness or injury, or taking certain medicines.
A doctor will consider your full blood count results alongside your symptoms, any conditions you have and any treatment you're having when deciding if any of your results might be a sign of a problem.
What happens after getting your full blood count results
If a doctor thinks your full blood count results might be a sign of a problem, what happens next depends on what the problem might be.
For example, a doctor may talk to you about:
- having more tests to find out what might be causing your results to be too low or too high
- changing or stopping any treatments or medicines that could be affecting your blood cells
- making changes to your diet or taking supplements (for example, taking iron supplements if your iron levels are low)