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Which blood count tool do you need?
The complete blood count (CBC) – called a full blood count (FBC) in the UK – is one of the most frequently ordered blood tests. It measures red cells, white cells and platelets, plus a set of red-cell indices. The tools in this section help you make sense of it:
- [CBC blood test explainer](/cbc-blood-test) – enter some or all of your CBC values to see how each compares with typical adult ranges, with explanations of every line on the report, including the white-cell differential.
- [MCV calculator](/mcv-blood-test) – calculates mean corpuscular volume from haematocrit and red cell count, classifies it as microcytic, normocytic or macrocytic, and shows the Mentzer index for small red cells.
- [Hemoglobin converter](/hemoglobin-g-dl-to-g-l) – converts haemoglobin between g/dL (US) and g/L (UK, Europe, Australia), and explains the mmol/L units used in a few countries.
The CBC at a glance
| Test | Typical adult range (US units) | What it tells you |
|---|---|---|
| Haemoglobin – men | 13.5–17.5 g/dL | Oxygen-carrying capacity; low = anaemia |
| Haemoglobin – women | 12.0–16.0 g/dL | As above |
| White blood cells | 4,500–11,000 /µL | Infection, inflammation, bone marrow activity |
| Platelets | 150,000–400,000 /µL | Clotting; low or high counts both need context |
| MCV | 80–100 fL | Average red cell size – the key to classifying anaemia |
| RDW | About 11.5–14.5% | Variation in red cell size |
These are typical ranges used in medical education; your laboratory's own reference range is the one that applies to your result. Ranges differ in children and in pregnancy.
How to approach an abnormal CBC
- Look at haemoglobin first. If it is low, you have anaemia; the next question is why.
- Use the MCV to narrow the cause. A low MCV (microcytic) points towards iron deficiency or thalassaemia trait; a high MCV (macrocytic) towards vitamin B12 or folate deficiency, alcohol, liver or thyroid disease, or some medicines; a normal MCV towards blood loss, kidney disease, inflammation or mixed causes.
- Check the RDW. A high RDW alongside a low MCV is typical of iron deficiency, while a normal RDW with a low MCV and high red cell count suggests thalassaemia trait.
- Read the white cells and platelets in context. A raised white count is most often due to infection or inflammation; the differential shows which white cells are affected.
- Compare with previous results. A stable, slightly abnormal value is often less concerning than a rapid change.
Iron, B12 and folate: the follow-up tests
Most abnormal red-cell results lead to further tests:
- Ferritin and an iron panel for a low MCV – see the low ferritin checker and the TIBC and iron panel calculator.
- Vitamin B12 and folate for a high MCV – see the vitamin B12 converter and folate converter.
- Reticulocyte count to see whether the bone marrow is responding to anaemia.
When a CBC needs urgent attention
Very low haemoglobin, very low or very high white cell counts, very low platelets, or the presence of immature cells (blasts) on the differential need prompt medical review – laboratories usually phone these results to the requesting clinician. If you feel very unwell, are short of breath at rest, have chest pain, unexplained bruising or bleeding, or a high fever, seek urgent care rather than waiting for a routine appointment.