A full blood count (FBC), also called a complete blood count (CBC), is a group of measurements about the cells in your blood. UK reports commonly show haemoglobin in g/L and cell counts in ×10^9/L, but the value, unit, date and reference interval printed on your own report always come first.
An FBC can provide clues for a clinician, but a high or low flag is not a diagnosis. Age, sex, pregnancy, symptoms, recent illness, medicines, previous results and the laboratory method can all change how the pattern is understood.
Key FBC components on a UK report
| Haemoglobin (Hb) | Usually g/L | The oxygen-carrying protein in red cells; use your report's interval |
|---|---|---|
| White blood cells (WBC) | Usually ×10^9/L | Includes immune cells; the differential may show types separately |
| Platelets | Usually ×10^9/L | Cell fragments involved in clotting; read with symptoms and the wider FBC |
| MCV, MCH and related indices | Use the printed units and ranges | Describe red-cell size and haemoglobin content; patterns are more useful than one flag |
Do not replace the range on your report with a universal table. Laboratory intervals vary with method and population, and a flag is a prompt for review rather than a diagnosis.
How to read the red-cell part of an FBC
Haemoglobin, red-cell count, haematocrit and indices such as MCV and MCH are read together. A pattern may lead a clinician to ask about iron stores, vitamin status, bleeding, inflammation, pregnancy or other context, but an FBC alone cannot establish the cause.
Use the value, unit, date and printed interval. A result that is close to the boundary, different from your previous result or flagged alongside other values may deserve discussion even when it does not look dramatic.
White cells and the differential
The white-cell count may be reported with a differential showing neutrophils, lymphocytes, monocytes, eosinophils and basophils. Recent infection, inflammation, medicines, stress and many other factors can affect these numbers, so a pattern is not a diagnosis of infection or another condition.
Platelets and the wider report
Platelets are involved in clotting. A flagged platelet result should be considered with bleeding or clotting symptoms, other blood counts, medicines and previous results. Avoid deciding what it means from a single number or from a generic online cut-off.
Useful appointment questions include: which values are genuinely outside this laboratory's interval, how do they compare with previous results, and is any follow-up needed for the pattern rather than one isolated flag?
When to contact your healthcare team
- If the report says critical, panic or urgent, contact the responsible clinical team according to the report's instructions.
- Seek appropriate urgent care for severe or worsening breathlessness, fainting, uncontrolled bleeding or other serious symptoms.
- For a non-urgent flag, bring the complete FBC and previous results to the ordering clinician; do not diagnose anaemia, infection or a blood disorder from one report.
- Mention pregnancy, recent illness, medicines, supplements and any bleeding or infection symptoms when discussing the result.
Common questions
Is FBC the same as CBC?
They describe the same broad blood-count panel. FBC is the term commonly used in the UK, while CBC is common in the US and some other settings.
Do I need to fast for an FBC?
Usually not. If the blood draw includes other tests, follow the preparation instructions from the ordering service because those tests may have different requirements.
Does one low haemoglobin result prove anaemia?
No. The result needs the laboratory's interval, the rest of the FBC, previous results and clinical context. A clinician should interpret the pattern and decide whether further assessment is appropriate.
Related guides
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Medical disclaimer: Educational only; not medical advice, diagnosis, or treatment. AI-generated interpretations are not reviewed by a physician or human clinician. Do not use this content for emergencies; consult a qualified healthcare professional. Do not post personal laboratory results publicly. Reference intervals vary between laboratories—use the value, unit, date and range printed on your own report, and consult a qualified healthcare professional about your results and symptoms.