What a full blood count (FBC) actually tells you

If you've ever had blood taken at a GP surgery or hospital, chances are a full blood count was part of the request. It's a broad screening test that looks at the cells circulating in your blood — and it can flag a surprisingly wide range of issues from a single sample.

What does an FBC measure?

A full blood count examines three main types of blood cell, each with several components:

Red blood cells

• Haemoglobin (Hb) — the protein that carries oxygen; low haemoglobin indicates anaemia
• Haematocrit (HCT) — the proportion of blood made up of red cells
• MCV (mean cell volume) — the size of red blood cells, which helps identify the type of anaemia

White blood cells

• Total WBC count — raised levels can indicate infection, inflammation or, rarely, blood disorders; very low levels can flag immune problems
• Differential — a breakdown into neutrophils, lymphocytes, monocytes and others, each associated with different conditions

Platelets

• These are the cell fragments involved in clotting; too few (thrombocytopenia) can cause bruising and bleeding; too many can increase clotting risk

What conditions can an FBC detect?

An FBC won't diagnose a specific condition on its own — but it can point in useful directions. Abnormal results might prompt investigation into:

• Anaemia — whether iron-deficiency, B12/folate-related, or due to chronic disease
• Infection or inflammation — raised white cells, particularly neutrophils, often reflect bacterial infection
• Viral illness — lymphocytes are typically elevated in viral infections
• Blood disorders — unusual patterns in any of the cell counts can prompt specialist review, though most abnormal results have far more common explanations

What an FBC doesn't tell you

An FBC is a starting point, not a complete picture. It doesn't assess iron stores directly (that requires separate iron studies), doesn't measure vitamin levels, and doesn't assess kidney, liver or thyroid function — those need additional panels. A normal FBC doesn't mean all is well with your health; it means the cell counts being measured are within the expected range.

How results are interpreted

Reference ranges on blood test reports can look alarming if you don't know what you're reading. A result marked as slightly outside the normal range isn't automatically a problem — context matters enormously. Age, sex, hydration status and the reason the test was ordered all affect how a GP interprets a result.

This is why a GP review of results is part of every blood test at Northwest Health. You'll receive your results alongside an explanation, not just a list of numbers to interpret yourself.

Getting an FBC privately in Preston

You don't need a referral to request a blood test at Northwest Health. An FBC is included in our Silver (£200), Gold (£350) and Platinum (£500) blood screens, alongside a range of other markers. Results are reviewed by a GP and typically returned within a few working days.

See what's included in our blood screens →