What the test measures
A complete blood count is one of the most commonly ordered blood tests. The panel usually includes:
- Red blood cells, which carry oxygen, together with haemoglobin (the oxygen-carrying protein) and haematocrit (the share of blood made up of red cells).
- White blood cells, part of the immune system; a "differential" counts the different types.
- Platelets, which help blood to clot.
- Cell-size measures, such as the average size of red cells.
Why it is ordered
A CBC can be part of a routine check-up, or help a clinician look into symptoms such as tiredness, infection or bruising, or follow a known condition or treatment.
Reading the report
- Each value is shown next to a reference range. Ranges can differ between laboratories and between patient groups.
- A value slightly outside the range can be normal for some people; see why reference ranges are not verdicts.
- Discuss unexpected results with the clinician who ordered the test — they can combine the numbers with your history and examination.
Sources
- Complete Blood Count (CBC) — MedlinePlus — U.S. National Library of Medicine. Checked 2026-07-13.
Editorial update: 2026-09-26.
Medical disclaimer: this is a source-linked educational summary, not individual medical advice, diagnosis, prescription or interpretation of personal results. For severe or rapidly worsening symptoms, call 115.
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