White Blood Cells
White Blood Cell Count (WBC)
What this test measures
White blood cells are part of your immune system. They help your body fight infections and disease. This test counts how many white blood cells are in your blood.
Understanding the numbers
Typical range: 4.0-11.0 × 10⁹/L
Levels can rise temporarily when you are fighting an infection.
- Very low: 0–2 × 10⁹/L
- Low: 2–4 × 10⁹/L
- Normal: 4–11 × 10⁹/L
- Mildly raised: 11–20 × 10⁹/L
- Markedly raised: 20–40 × 10⁹/L
Key numbers
- 4 × 10⁹/L — Lower limit of normal
- 11 × 10⁹/L — Upper limit of normal
- 2 × 10⁹/L — Below = risk of serious infection; urgent review
Typical UK laboratory reference range. A very low white count (particularly low neutrophils) makes serious infection more likely; a very high count with symptoms needs urgent assessment. The differential (neutrophils vs lymphocytes) usually tells more than the total count.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean
- Your body may be fighting an infection
- Can happen with inflammation or allergies
- Stress or certain medicines can raise levels
- Very high levels need further investigation
When not to wait
A very low white count with fever, or a very high count with severe illness, needs urgent review.
- Fever of 38°C or higher if you're on chemotherapy or known to have low white cells
- Uncontrollable shaking or feeling cold to the bone
- Confusion, drowsiness, or feeling extremely unwell
- Fast breathing, low blood pressure, or pale clammy skin
- New mouth ulcers, severe sore throat with swollen tongue
- Unexplained severe bruising or bleeding alongside infection
Call NHS 111 for urgent advice, or 999 if someone is seriously unwell.
Questions you could ask your GP
- Is my white cell count likely due to an infection, or could there be another cause?
- Do I need a repeat blood test to check if my levels return to normal?
- Should I take any precautions to avoid infections while my count is low?
- Do I need to see a specialist about my white blood cell count?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Sore throat, swollen glands
Aisha had a sore throat, fever, and swollen glands in her neck. Her WBC was 14.2 × 10⁹/L with a raised lymphocyte count. A monospot test was positive.
What the GP said: “This is glandular fever (infectious mononucleosis) — the raised white count is your body fighting the Epstein-Barr virus. It usually settles in a few weeks. Rest, fluids, paracetamol — and please avoid contact sport for about a month because your spleen can be a bit enlarged.”
What happened next: Aisha's energy came back over six weeks. Her repeat blood count was normal at two months.
A raised white count is usually a sign your immune system is working, not failing. The shape of the rise (mainly lymphocytes vs mainly neutrophils) helps the GP decide whether it's viral, bacterial, or something else.
Fever, cough, feeling very unwell
Gareth presented with a fever of 39°C, shortness of breath and a productive cough. His WBC was 22 × 10⁹/L (mostly neutrophils) and his CRP was 180.
What the GP said: “This looks like severe pneumonia. Your oxygen levels are a bit low and your CURB-65 score is high — I'm admitting you to hospital for IV antibiotics and oxygen.”
What happened next: Gareth had a four-day admission, IV co-amoxiclav then oral step-down. His WBC normalised over two weeks.
A sharply raised white count with fever and a clear source points to a serious bacterial infection. Early antibiotics and hospital treatment can be life-saving in pneumonia, especially in older adults.
Chemotherapy — low counts expected
Stephanie is on chemotherapy for breast cancer. Ten days after her third cycle her WBC was 1.8 × 10⁹/L with neutrophils of 0.4 — she felt well.
What the GP said: “This is expected with your chemotherapy, but it means you're at risk of serious infection without typical warning. You have your chemo helpline card — phone them immediately if you get a fever of 38 or higher, feel shaky, or feel unusually unwell.”
What happened next: Stephanie's counts recovered by day 14 and her next cycle went ahead on time. She kept the helpline number on her fridge.
A very low white count — especially low neutrophils — after chemo is expected but dangerous. A fever in this state is a medical emergency: do not wait, do not try to manage at home.
Routine screen, unexpected finding
Bhaskar's WBC was 38 × 10⁹/L on a routine check. He felt well. The differential showed almost all were mature lymphocytes.
What the GP said: “A persistent very high lymphocyte count in someone your age can be chronic lymphocytic leukaemia — a slow-growing type that often doesn't need treatment for years. I'm referring you urgently to haematology for confirmation.”
What happened next: Haematology confirmed CLL — early stage. Bhaskar was placed on 'watch and wait', with six-monthly reviews. After three years his counts were stable and he still hadn't needed treatment.
A very high white count without illness is sometimes the first sign of a blood cancer like CLL. Not all blood cancers need treatment immediately; CLL in particular is often monitored for years without harm.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.