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Full blood count results explained
A full blood count (FBC, also called CBC) measures your red cells, white cells and platelets. Here is what each abbreviation means and what high or low values can indicate.
This guide is general information and does not replace medical advice. Reference ranges differ between laboratories – always compare your result with the range printed on your own report and discuss abnormal results with a doctor.
A full blood count (FBC) – in many countries called a complete blood count (CBC) – is the most frequently requested blood test. It counts and measures the three main cell types in your blood: red blood cells that carry oxygen, white blood cells that fight infection and platelets that help blood clot.
Full blood count abbreviations and typical adult ranges
The ranges below are typical values for adults used by many UK laboratories. Your laboratory may use slightly different limits and units.
| Abbreviation | What it measures | Typical adult range |
|---|---|---|
| Hb (haemoglobin) | Oxygen-carrying protein | Men 130–180 g/L; women 115–165 g/L |
| RBC | Red blood cell count | Men 4.5–6.5 ×1012/L; women 3.8–5.8 ×1012/L |
| HCT / PCV | Share of blood volume made up of red cells | Men 0.40–0.54; women 0.37–0.47 |
| MCV | Average red cell size | 80–100 fL |
| MCH | Average haemoglobin per red cell | 27–32 pg |
| MCHC | Haemoglobin concentration in red cells | 320–360 g/L |
| RDW | Variation in red cell size | 11.5–15 % |
| WBC | White blood cell count | 4.0–11.0 ×109/L |
| Neutrophils | Fight bacterial infection | 2.0–7.5 ×109/L |
| Lymphocytes | Fight viral infection, immunity | 1.0–4.0 ×109/L |
| Monocytes | Clean up debris, chronic inflammation | 0.2–0.8 ×109/L |
| Eosinophils | Allergy, parasites | 0.04–0.4 ×109/L |
| Basophils | Allergic reactions | 0.0–0.1 ×109/L |
| PLT | Platelet count | 150–400 ×109/L |
Low haemoglobin (anaemia)
Haemoglobin below the range means anaemia. Common symptoms are tiredness, shortness of breath and pale skin. The red cell indices help find the cause:
- Low MCV (small cells) – most often iron deficiency (for example heavy periods, low iron intake or blood loss from the gut); thalassaemia trait is another cause.
- High MCV (large cells) – vitamin B12 or folate deficiency, regular alcohol use, liver disease, an underactive thyroid or some medicines.
- Normal MCV – chronic illness, kidney disease, recent bleeding or a mixed cause.
High haemoglobin can be caused by dehydration, smoking, living at altitude, lung disease or, rarely, a bone marrow condition.
High or low white blood cells
A high WBC is most often caused by infection, inflammation, physical stress, smoking or steroid medicines. The differential shows which type is raised: neutrophils typically rise with bacterial infection, lymphocytes with viral infection, eosinophils with allergy, asthma or parasites.
A low WBC can follow a viral infection and often recovers within a few weeks. It can also be caused by some medicines, autoimmune conditions or B12 and folate deficiency. Some people of African, Middle Eastern or Caribbean ancestry naturally have lower neutrophil counts without any illness.
High or low platelets
High platelets are usually a reaction to infection, inflammation, iron deficiency or bleeding. Low platelets can be caused by viral infections, alcohol, some medicines, liver disease or immune conditions. Very low platelets (below about 20–30 ×109/L) increase the risk of bleeding.
When should you see a doctor?
- if several values are abnormal together, or a value is far outside the range;
- if you have symptoms such as marked tiredness, breathlessness, unexplained bruising or bleeding, recurring infections, fever, night sweats or weight loss;
- if an abnormal value does not return to normal on a repeat test.
Seek urgent care if you have heavy or uncontrolled bleeding, fever with a very low white cell count, chest pain or severe breathlessness.
Sources
- NHS – Blood tests: nhs.uk/conditions/blood-tests
- NHS – Iron deficiency anaemia: nhs.uk/conditions/iron-deficiency-anaemia
- Lab Tests Online UK – Full blood count: labtestsonline.org.uk
- NICE Clinical Knowledge Summaries – Anaemia, iron deficiency: cks.nice.org.uk
Frequently asked questions
Is a slightly abnormal full blood count dangerous?
Not usually. Results just outside the reference range are common in healthy people – about 1 in 20 healthy results falls outside a range by definition. What matters is how far outside, whether several values are abnormal together, your symptoms and the trend over time.
Do I need to fast before a full blood count?
No. A full blood count does not require fasting, but tell the laboratory about recent illness, heavy exercise or medicines, because they can temporarily change white cell and platelet counts.
What does a low MCV mean?
A low MCV means the red blood cells are smaller than usual (microcytosis). The most common cause is iron deficiency; thalassaemia trait is another. Ferritin is usually checked next.