A full blood count (FBC), called a complete blood count (CBC) in the US, measures the three types of cells in your blood: red cells that carry oxygen, white cells that fight infection, and platelets that help blood clot. It can show anaemia, signs of infection or inflammation, and some bone marrow problems, but it does not check your liver, kidneys, cholesterol, sugar or thyroid.
| Category | Reference range |
|---|---|
| Haemoglobin, women | 120–150 g/L (12.0–15.0 g/dL) UK units (US units in brackets) |
| Haemoglobin, men | 130–170 g/L (13.0–17.0 g/dL) UK units (US units in brackets) |
| White cell count (WBC) | 4.0–11.0 ×10⁹/L (4.0–11.0 K/µL) UK units (US units in brackets) |
| Platelets (PLT) | 150–400 ×10⁹/L (150–400 K/µL) UK units (US units in brackets) |
| MCV | about 80–100 fL UK units (US units in brackets) |
Typical adult ranges; every lab sets its own, so use the range printed on your report.
The test needs one small tube of blood (usually a purple-top EDTA tube) and no fasting. An analyser counts and sizes the cells and prints around 15 to 25 lines.
A full blood count is not a cancer screening test. It can raise suspicion of blood cancers such as leukaemia, which often change the white cell count and may lower haemoglobin and platelets at the same time, but a normal FBC does not rule out most other cancers. Bowel cancer, for example, may show only as iron-deficiency anaemia, or not at all.
Equally, an abnormal count is far more often caused by infection, iron deficiency or a medicine than by cancer. If something is unclear, the usual next step is a repeat test or a blood film examined by a specialist.
Look first at the three headline numbers: haemoglobin, white cell count and platelets. Then use the details. A low haemoglobin with low MCV suggests a different cause from a low haemoglobin with high MCV. A normal total white count can still hide a low neutrophil count, so check the absolute values in the differential, not only the percentages.
Unit differences between countries are mostly cosmetic: ×10⁹/L in the UK and K/µL in the US give the same number for white cells and platelets. For haemoglobin, 120 g/L equals 12.0 g/dL. Small deviations in one line, with everything else normal, are common and often just repeated.
Your GP or doctor will usually go through flagged results at a routine appointment. Get help the same day (NHS 111, urgent care, A&E or the emergency room) if an abnormal count comes with:
Written using public information from:
No need to decode the numbers yourself: take a photo of the report and the app explains “What a full blood count shows” and the rest in plain words — what is normal and what deserves attention.
App StoreGoogle PlayWeb versionYour red cells and haemoglobin, white cells and platelets. It helps detect anaemia, infection, inflammation, some effects of medicines and blood disorders. It does not test organs such as the liver, kidneys or thyroid.
Yes. Full blood count is the UK name and complete blood count is the US name for the same test. A "CBC with differential" includes the breakdown of white cell types.
No. An FBC is not affected by eating. You may be asked to fast only if other tests, such as glucose or a lipid profile, are taken from the same sample.
No. Diabetes is checked with HbA1c or a glucose test, which are separate. Your doctor often requests them at the same time, so they may appear on the same report.
Some blood cancers change the counts, but many other cancers do not. A normal FBC does not exclude cancer, and an abnormal one is usually due to something much more common.
This material is for general information only. It is not a medical opinion and does not replace a consultation with a doctor. Reference ranges depend on the laboratory and the method — rely on the range printed on your own report. Your doctor makes the final interpretation.
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