The full blood count — often shortened to FBC (or CBC in some countries) — is the most commonly ordered blood test in the world. From a single sample it examines the three main types of cell floating in your blood, giving a remarkably broad snapshot of your health. Here's what it's actually looking at, and what the results can hint towards.
The three cell lines it checks
Your blood contains three families of cells, and the FBC counts and measures all of them:
- Red blood cells — carry oxygen around your body.
- White blood cells — your immune system's front line against infection.
- Platelets — tiny fragments that help your blood clot.
Each family has its own set of measurements, which is why an FBC report can list 15 or more individual values.
Red cells: oxygen and anaemia
The key red-cell markers are haemoglobin (the oxygen-carrying protein) and MCV (the average size of your red cells). A low haemoglobin points to anaemia, and the MCV helps identify the type: small cells often suggest iron deficiency, while large cells can point towards a B12 or folate deficiency. A high red-cell count is less common and has its own set of causes your doctor would explore.
White cells: infection and immunity
White cells rise and fall in response to what your body is dealing with. A raised white-cell count commonly reflects a bacterial infection or inflammation, while a low count can follow certain viral infections or be a side effect of some medications. The FBC also breaks white cells into subtypes (such as neutrophils and lymphocytes), and the pattern between them can give further clues.
Platelets: clotting
Platelets help you stop bleeding. Too few can be linked to easy bruising or bleeding, while a high count can occur temporarily after infection, inflammation or blood loss. As with the other cell lines, the number is a starting point rather than a diagnosis on its own.
Why it's such a common starting point
Because it touches on oxygen delivery, immune activity and clotting all at once, the FBC is a natural first test for a huge range of symptoms — tiredness, recurrent infections, unexplained bruising, breathlessness and more. It's quick, inexpensive and often the test that tells your doctor where to focus next.
Book a full blood count
Our FBC measures your red cells, white cells and platelets — a broad, low-cost snapshot that's a sensible starting point for tiredness, infections and general health checks.
Book a full blood countWhat your results mean
It's common for one or two values to sit slightly outside the "normal range" without anything being wrong — ranges are based on averages, and normal varies between people. A result that's flagged usually needs context, not panic: your doctor interprets it alongside your symptoms, your history and sometimes a repeat test before drawing any conclusion. A single mildly abnormal number is rarely the whole story.
When to get checked
An FBC is worth considering if you're persistently tired, keep picking up infections, are bruising easily, or simply want a baseline as part of a general check-up. It's one of the most informative tests available for the time and cost involved.
Book a full blood count with OneMedicine
Book online with OneMedicine — CQC-registered clinic in Birmingham, or a home visit / local clinic nationwide. Doctor-reviewed results, most within 24 hours.
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Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic