High white blood cells: what it means and what to do

When your white blood cells are above your report’s limit, there is often an infection or inflammation going on. But smoking, stress, a hard workout and cortisone raise them too. To find the cause, doctors look at which type of white cell has gone up: only rarely is it a blood disorder.

What high white blood cells mean

White blood cells are the cells of your immune defences. They rise when your body fights an infection or inflammation. But they also rise for reasons that have nothing to do with it, such as smoking, stress or intense exercise.

The total shows that your defences are busy, not what they are fighting. To find out, doctors look at the differential: which type of white cell has gone up. Often it is the neutrophils.

What causes high white blood cells

The first is the most common. Many of them do not mean a disease.

• An infection: White cells rise to fight it, and usually come back down once you recover.
• Lasting inflammation: For example some forms of arthritis or an inflammatory bowel disease.
• Smoking and extra weight: People who smoke often have higher counts, and so, a little, do people who are overweight. After quitting smoking, they usually come down within a year.
• Stress or intense exercise: Strong stress or a hard workout raises them for a few hours, even without an infection.
• Cortisone and pregnancy: Cortisone and some other medicines push them up. In pregnancy they rise a little, which is normal.
• A blood disorder, rarely: Such as leukaemia. It is rare, and your doctor looks for it with other tests if the count stays high for no clear reason.

Symptoms

High white blood cells cause no symptoms on their own. Any symptoms come from the cause: with an infection, for example, fever, a sore throat, a cough or burning when you pass urine.

If you have night sweats, lose weight for no reason or have swollen glands that do not go away, talk to your doctor.

High white blood cells with no symptoms

This happens a lot. Smoking, stress or a workout the day before is enough to raise them, even when you feel fine. Sometimes your body is still finishing off an infection that has just passed.

If the count is only slightly above the limit, your doctor usually has it repeated later, away from infections and hard exercise. If it stays high for no clear reason, your doctor looks at the differential and may ask for more tests: rarely, a blood disorder is behind it.

Which tests to read alongside it

These tests help find the cause.

What your result means

The upper end of the scale, in x10⁹/L.

• Within your report’s limits, Usually 4 to 11: Normal. Usually fine. But the total does not show which white cells are there. In the Rosa report you also see whether you are in your optimal range.
• Above your report’s limit, Usually above 11: High. An infection, smoking, stress or a hard workout is often behind it. Show your report to your doctor, who decides whether to repeat the test. If they are very high, or you have a fever with strong shivers, see a doctor the same day.

What to do if they are high

It starts with the cause: once it passes, they usually come down on their own. Where to start:

• Show your report to your doctor: they decide whether to repeat the test, usually once any infection has passed.
• Arrive at the next blood test rested, without a hard workout the day before.
• If you smoke, quitting brings them down, usually within a year.
• If you take cortisone or other medicines, tell your doctor, and do not stop them on your own.
• What to eat: you do not need a special diet. What counts is removing the cause.

When to worry

Talk to your doctor if:

• They stay high on a repeat test, with no clear reason.
• They are very high, even if you feel well: see a doctor the same day.
• They are high and your haemoglobin or platelets are out of range too.
• You have night sweats, lose weight for no reason, bruise easily or have swollen glands in your neck, armpits or groin.
• You have a fever with strong shivers: see a doctor the same day.
• You have a fever and feel confused, breathless or faint: call 112 or go to the emergency department.

Frequently asked questions

Slightly high white blood cells: should I worry? Usually not, if you feel well and the rest of your blood count is normal. A recent infection, smoking, stress or a workout is often behind it. Show your report to your doctor, who decides whether to repeat the test.

Can high white blood cells mean leukaemia? Rarely. Much more often an infection, inflammation, smoking or stress is behind it. If the count stays high for no reason, your doctor looks at the differential and, if needed, asks for more tests.

High CRP and high white blood cells: what does it mean? Together they point to an infection or inflammation going on, and your doctor looks for the cause starting from your symptoms. With a fever and strong shivers, see a doctor the same day.

Does exercise raise white blood cells? Yes, briefly. Intense exercise raises them for a few hours, then they go back to where they were. That is why it is best not to train hard the day before a blood test.

Is it normal for them to be high in pregnancy? A little, yes: in pregnancy they rise gradually, especially towards the end. If you have a fever, see a doctor the same day.

Sources

• Riley and Rupert, evaluation of patients with a high white blood cell count. American Family Physician, 2015. PMID 26760415
• European Hematology Association and EuNet-INNOCHRON, European guidelines on the diagnosis and management of neutropenia in adults and children. HemaSphere, 2023. PMID 37008163
• Newburger and Dale, evaluation and management of patients with isolated neutropenia. Seminars in Hematology, 2013. PMID 23953336
• Higuchi and colleagues, current smoking as a reversible cause of a raised white blood cell count in healthy adults. Preventive Medicine Reports, 2016. PMID 27583199
• Merz and colleagues, absolute neutrophil count by Duffy status in healthy Black adults. Blood Advances, 2023. PMID 35994632