Quick answer
What is a full blood count?
A full blood count (FBC) is a blood test that measures red cells, white cells and platelets, helping to detect anaemia, infection and other blood disorders. It needs no fasting or special preparation. Your GP explains any abnormal results alongside your symptoms and medical history.
What a full blood count measures
A full blood count looks at three main components of your blood. Red cells carry oxygen around the body, white cells help fight infection, and platelets allow the blood to clot properly. Each component is reported alongside a reference range so you and your GP can see whether your results fall within the expected limits.
Common abnormalities on a full blood count
The most frequent findings on a full blood count are anaemia, signs of infection, and thrombocytopenia, which is a low platelet count. Any of these results usually prompts further tests to clarify the underlying cause rather than a diagnosis from the blood count alone.
When a full blood count is used
A full blood count is commonly requested when someone reports tiredness, unusual bruising or signs of infection. It is also used before surgery and to monitor the effects of certain medicines. Many people also have one done as part of a routine health check even without symptoms.
Next steps after a full blood count
Your GP will look at your full blood count alongside a physical examination and your medical history to decide what it means for you. If an abnormality persists, they may arrange a repeat test or refer you to a specialist for further investigation.
Common questions about the full blood count
- What does anaemia on a full blood count mean?
- Anaemia on a full blood count means your haemoglobin level is lower than normal, which can cause tiredness and breathlessness. Iron deficiency is a common cause, so further tests are usually done to find out why.
- What does a high white cell count mean?
- A high white cell count is often a sign that the body is fighting an infection. Less commonly it can point to conditions such as leukaemia, so a repeat test and specialist assessment may be needed to rule this out.
- What does a low platelet count mean?
- A low platelet count means you may bruise or bleed more easily than usual. It has many possible causes, ranging from viral infections to certain medicines, so your GP will look for the underlying reason.
- Do I need to fast before a full blood count?
- No, you do not need to fast before a full blood count. The test can be taken at any time of day regardless of when you last ate.