What does a high white blood cell count mean?
Usually your body reacting to an illness, like an infection. Smoking, steroids and pregnancy raise it too. But the total is half the story. Which white cell is high says more.
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Is a white cell count of 11, 12 or 15 high?
At most NHS labs, yes if it’s above 11.0. The usual adult range is 4.0 to 11.0. The unit, x10⁹/L, means billions of white cells in each litre of blood.
Some set the top line lower. One private lab stops at 10.0, so a 10.5 can be high on one sheet and fine on another. A 12 or 15 is above every UK lab range in that list.
- Below 4 x10⁹/LBelow most NHS labs’ range.
- 4 up to 11 x10⁹/LIn range at most NHS labs.
- Above 11 up to 20 x10⁹/LAbove range. Usually a reaction to illness.
- Above 20 x10⁹/LNHS guide: consider referral if it stays above 20 with no cause.
Sources: Severn Pathology (North Bristol NHS); UK reference ranges study; BNSSG NHS referral guide
Think of white cells as fire engines. More on the road means something called them out.
More engines doesn’t mean a big fire. One NHS guide for GPs says a raised count is most commonly a normal response to illness. Your GP’s job is to find what called them.
Your next move: check the range printed beside your result, then look at the lines under the total.
What causes a high white blood cell count?
| Reason | Examples |
|---|---|
| Infection | Bacteria or viruses |
| Inflammation | Swelling and soreness inside the body, such as rheumatoid arthritis |
| Damage to the body | A burn, surgery, or tissue starved of blood |
| Allergy | An allergic reaction |
| Everyday causes | Smoking, stress, pregnancy, or medicines such as steroids |
| Blood cancers (rare) | Leukaemia or Hodgkin lymphoma |
Sources: MedlinePlus; BNSSG NHS referral guide; North West London Pathology (NHS)
Smoke? One NHS guide says smoking commonly causes a mild rise.
Another says a mild, lasting rise in neutrophils, under 15, is most likely from long-term inflammation or infection. It may be linked to smoking.
Hard exercise counts too. In a small study of 10 young men, a 30-second all-out sprint raised white cells by 40%. An hour later, they were below where they started.
On steroids or another regular medicine? Mention it when you discuss the result. Never stop or change a prescribed medicine without your prescriber.
Ill or training hard before the test? See being ill before a blood test and exercise before a blood test.
Which white cells are high?
This is the other half of the story. Your total is split into types in the lines below it. That split is called the differential.
| Type | Range at one NHS lab | What often raises it |
|---|---|---|
| Neutrophils | 1.5 to 8.0 | Bacterial infection most of all. Also inflammation, steroids, pregnancy and smoking. |
| Lymphocytes | 1.0 to 4.0 | Viral infections, especially glandular fever. Smoking too. |
| Monocytes | 0.2 to 1.0 | Inflammation or infection. |
Sources: Severn Pathology (North Bristol NHS); BNSSG NHS referral guide; MedlinePlus
Neutrophils mostly target bacteria. Lymphocytes mostly target viruses.
Neutrophils and lymphocytes both up? Then a reaction to illness is more likely than a blood disorder, says the same NHS guide.
No breakdown on your sheet? Ask your GP whether a differential was done. More lines are explained in our full blood count guide.
Could a high white cell count be leukaemia?
Usually not. A high neutrophil count is rarely caused by a blood disorder, says one NHS guide.
A long-lasting rise in lymphocytes is typical of one blood cancer, chronic lymphocytic leukaemia (CLL). CLL is most common between 60 and 80, and very rare under 40.
The NHS says CLL usually develops very slowly and doesn’t always need treatment straight away. Many people with it have no symptoms.
What makes a GP look harder is the pattern, not one number.
That means a count that keeps rising. Or low haemoglobin (the part that carries oxygen) or platelets (the cells that help blood clot) as well. It also means feeling very unwell, sweats, fevers, weight loss or itching, or a swollen spleen (an organ under your left ribs) or glands.
What happens after a high WBC result?
What one NHS guide tells GPs to do
- 1
Find the type
Check which white cells are high. Looking at your blood under a microscope (a blood film) and CRP help.
- 2
Treat the cause
If there’s an infection or inflammation, treat that first.
- 3
Repeat the count
After you recover. High lymphocytes: usually 4 to 6 weeks.
- 4
Consider referral
A count above 20 that stays high, or neutrophils above 15, with no cause.
Source: BNSSG NHS referral guide
CRP is a blood test for inflammation. See our CRP blood test guide.
Don’t need a referral? The guide suggests a repeat count in 3 months, or sooner if things change. Above 100, it tells the GP to phone the on-call blood specialist.
Before your repeat white cell count
- Tell your GP about any recent infection, injury or operation.
- Bring a list of your medicines, including any steroids.
- Say if you smoke or are pregnant.
- Skip a hard workout just before the test.
- Book the same time of day as your last test, so the two compare fairly.
- Write down any sweats, fevers, weight loss or itching to tell your GP.
Sources: BNSSG NHS referral guide; MedlinePlus; Nieman et al, 1992; UK reference ranges study
Comparing other lines too? See blood test reference ranges.
When to speak to a GP
Your GP reads your count with your symptoms, history and other results. Book an appointment soon if:
- You have paler skin, ongoing tiredness, a fever with no clear cause, or infections that keep coming back or won’t clear. For adults with these, NICE says to consider a very urgent full blood count.
- You have swollen glands in several places, bruising or bleeding with no clear cause, or tiny red or purple spots on your skin. These are on the same NICE list, along with a swollen liver or spleen.
- You have sweats, fevers, weight loss or itching with a high count. One NHS guide asks GPs to check for these.
- Your count is still high on a repeat test after you’ve recovered, and there’s no clear cause.
- Your count keeps rising between tests, or your haemoglobin or platelets are low too.
Call 999 or go to A&E if you’re breathing very fast, or confused, slurring or not making sense. Do the same for blue, pale or blotchy skin, or a rash that doesn’t fade when you press it.
A very high or very low temperature, feeling hot or cold to the touch, or shivering also counts. These can be signs of sepsis.
Worried it might be sepsis? Call 999 too.