What are leukocytes?
Your immune system consists of cells that are made in your bone marrow and travel through your blood to the place where they are needed. Together they are called white blood cells or leukocytes, and there are five types, each with its own task. Neutrophils are the largest group and attack bacteria, lymphocytes recognise viruses and remember them, monocytes clean up, eosinophils respond to allergy and parasites, and basophils are the smallest group and release histamine. The total count is the sum of those five. But only a small part of your white cells is in your blood at any moment. The rest lies ready in your bone marrow and along the wall of your blood vessels, and can be pushed into the bloodstream within minutes. That happens with stress, with hard exercise and with an infection: adrenaline and cortisol loosen the cells from the vessel wall and the bone marrow releases extra cells. That is why the count can double within an hour without more cells having been made, and falls just as fast again. Your report shows the count in ×10⁹/L, billions of cells per litre. Normal is about 4.3 to 10.0 ×10⁹/L, where the labs overlap. A report with only the total says little; the differential, the count per type, says whether it is about bacteria, a virus, an allergy or something else.
Why are leukocytes relevant?
The total of white blood cells is the first question in someone who is ill: is there an infection, and if so, which way is it going? A bacterium lifts the count through the neutrophils and usually goes with a high CRP; a virus often lets the total fall instead, while the lymphocytes rise. Those two patterns are so different that a blood count with differential often says more than the total. For anyone who is healthy, the count is interesting for another reason. A total that sits at the high end year after year, without an infection, is a sign of a body in a light inflammatory state. Smoking is the most common reason for that: smokers have persistently more white cells in their blood, and that corrects over months after stopping. Belly fat does the same in milder form, and poor sleep and long-term stress lift the count through cortisol. A higher total within the band therefore goes with more cardiovascular disease, not because the cells do harm, but because they show that the inflammation is there. A low total weighs more heavily than a high one. Below 4.0 ×10⁹/L you have fewer immune cells available, and if that is down to the neutrophils, you are more susceptible to bacteria. Usually the reason is harmless and temporary, a virus that has just passed or a medicine, and in some people a lower count is simply their make-up. If it stays low without explanation, or keeps falling, then a look at the bone marrow belongs with it.
Leukocytes reference ranges
What counts beside the number:
- The differential: which of the five types lifts or lowers the count
- CRP from the same draw, which says whether an infection is the cause
- Whether you were ill in the weeks before, and which medicines you take
- Whether you smoke, how you sleep and whether you trained hard the day before
- Your ancestry, because a lower neutrophil count is make-up in many people
- Haemoglobin and platelets from the same blood count, which say whether the bone marrow as a whole is working
The total only gains meaning with the differential alongside: neutrophils, lymphocytes, monocytes, eosinophils and basophils, each as an absolute count. Do not read it as a percentage, because a percentage also shifts when another type moves. Smokers sit structurally higher in the band, and a measurement straight after exertion or stress sits a few hours above your resting value.
What Dutch labs actually use
Rare for a blood value: all four of these labs put the upper bound at exactly 10.0. The difference sits only at the bottom, where three use 4.0 and Star-shl 4.3. A result landing in between is normal at one lab and low at another.
4.3 – 10.0×10⁹/L
Between 4.0 and 4.3 it depends on the lab, because each sets its limits on its own method and population. Above 10.0 every lab calls it abnormal.
every lab calls 4.3 – 10.0 ×10⁹/L normal. Between 4.0 and 4.3 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Above 15 yrs | 4.0–10.0 ×10⁹/L |
| Star-shl2026 | 18–110 yrs | 4.3–10.0 ×10⁹/L |
| Certe2026 | Women from 18 yrs | 4–10 ×10⁹/L |
| Men from 18 yrs | 4–10 ×10⁹/L | |
| Clinical Diagnostics2026 | Above 15 yrs | 4.0–10.0 ×10⁹/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Leukocytes high or low: what it means
A low total usually means the neutrophils have fallen, because they are the largest group. Look at the differential to see that. The most common reasons: a viral infection in the past weeks, which slows the bone marrow for a few days and keeps the count low for up to a few weeks, and medicines such as some painkillers, antibiotics, thyroid blockers and drugs for rheumatoid arthritis or epilepsy. In people with African or Middle Eastern ancestry the neutrophil count is naturally lower, without the immune system working any less well. A total that repeatedly stays below 4.0 ×10⁹/L without explanation, or together with anaemia and few platelets, calls for a look at the bone marrow. A high total means your body is mobilising cells, and the question is what for. With fever and a high CRP it is a bacterial infection or an inflammation. Without fever, stress, a hard training session the day before, a night of poor sleep, smoking, prednisone or a pregnancy are the most common explanations, and you see those in the differential as a rise in neutrophils without young forms. A total above 30.0 ×10⁹/L, or a rise in which the lab sees immature cells, is a different picture and is assessed the same day. What you do about it: with a rise from an infection nothing, the count falls with recovery. With a total that stays at the high end without an infection, stopping smoking is the biggest step, followed by less belly fat, better sleep and less chronic stress. Have blood drawn on a rest day and not straight after exercise, because that lifts the count for a few hours. With a low total from a medicine the question is whether that medicine stays necessary, and you discuss that with whoever prescribed it. Read the total beside the differential, because the five types each point a different way, and beside CRP, which says whether an infection is the cause. Platelets and haemoglobin from the same blood count show whether the bone marrow as a whole is working well.
What lowers it
There are fewer white cells in your blood, usually temporarily and usually through the neutrophils.
| Cause | How often |
|---|---|
| Viral infectionA virus slows the bone marrow for a few days and draws cells into the tissue; the total stays low for up to a few weeks after the infection | Often |
| MedicationSome painkillers, antibiotics, thyroid blockers and drugs for rheumatoid arthritis or epilepsy suppress production; after stopping, the count recovers | Often |
| Naturally lowIn people with African or Middle Eastern ancestry the neutrophil count is naturally lower, with an immune system that simply works | Sometimes |
| Autoimmune diseaseIn lupus or rheumatoid arthritis antibodies can break down white cells; then there are usually symptoms and other abnormalities too | Rare |
| Bone marrow problemIf production itself falters, haemoglobin and platelets usually fall along with it | Rare |
What raises it
Your body is mobilising cells, from the bone marrow or from the vessel wall, and the question is what for.
| Cause | How often |
|---|---|
| Bacterial infectionThe classic reason: the bone marrow releases extra neutrophils, and CRP rises along | Often |
| InflammationTissue damage, a flare of rheumatoid arthritis or a bowel inflammation give the same response as an infection | Often |
| Stress or hard exerciseAdrenaline and cortisol loosen cells from the vessel wall; the count can double within an hour and is back after a few hours | Often |
| CorticosteroidsPrednisone releases neutrophils from the bone marrow and keeps them in the blood; the total sits high during a course without an infection | Often |
| SmokingSmokers have persistently more white cells; after stopping, the count falls over months | Sometimes |
| Excess weightBelly fat keeps the body in a light inflammatory state and lifts the total a little | Sometimes |
| Bone marrow diseaseWith a total far above the band, with immature cells on the report, the bone marrow is making cells uncontrolled | Rare |
How does a leukocytes blood test work?
- Referral
- Not needed. The total of white blood cells is in every blood count, and you can have it measured yourself, preferably with the differential.
- Fasting
- Not needed; the count does not respond to food. It does respond to exertion and stress, so come to the draw calmly.
- When
- On a rest day, not the morning after a hard training session or a bad night, and not during or in the weeks just after an infection, unless you want to see exactly how the body responds to it.
- The draw
- One tube of blood from a vein in your arm. The lab counts the cells and sorts them into five types; haemoglobin and platelets come from the same tube.
- Repeating
- With a deviating value after two to four weeks, when you are well, to see whether it was a snapshot. Otherwise once a year, or sooner if you take a medicine that can slow the bone marrow.
- Which test
- Leukocytes is in the comprehensive test (€229) and in .
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What are leukocytes?
Your white blood cells, the cells of your immune system. There are five types: neutrophils against bacteria, lymphocytes against viruses, monocytes that clean up, eosinophils for allergy and parasites, and basophils that release histamine. They are made in your bone marrow and travel through your blood to where they are needed. The total is the sum of the five.
What is a normal leukocyte value?
Between 4.3 and 10.0 ×10⁹/L, where the four labs overlap; three labs already start at 4.0. A non-smoker usually sits in the lower half of that band. Only a small part of your white cells is in your blood at any moment, and stress, exertion and smoking push extra ones in, so the value on a calm morning is your true resting value.
What does a high leukocyte count mean?
That your body is mobilising cells. With fever and a high CRP it is a bacterial infection or an inflammation. Without fever, stress, a hard training session, poor sleep, smoking, prednisone or a pregnancy are the most common reasons; with stress the count can double within an hour. A total far above the band, in which the lab sees immature cells, is a different picture and is assessed the same day.
What does a low leukocyte count mean?
Usually that the neutrophils have fallen, through a virus that has just passed or through a medicine, and that recovers by itself. In some people, especially with African or Middle Eastern ancestry, the count is naturally lower, with an immune system that simply works. A low total weighs more heavily than a high one, because you have less defence against bacteria; if it stays low without explanation, or haemoglobin and platelets fall along, then an investigation of the bone marrow belongs with it.
Why does smoking lift the white blood cells?
Because smoke keeps the lungs and the vessel wall in a light, continuous inflammatory state, and the bone marrow answers that with more cells. Smokers therefore sit persistently higher in the band, often without passing the upper bound. Those extra cells are a sign of the inflammation, and that goes with more cardiovascular disease. After stopping, the count falls back over months.
How do I bring my leukocytes down?
With an infection you need do nothing; the count falls with recovery. With a total that stays at the high end without an infection, stopping smoking is the biggest step, followed by less belly fat, better sleep and less chronic stress. Have blood drawn on a rest day and not straight after exertion, because that lifts the count for a few hours without anything being wrong.
Why is the total alone not enough?
Because the five types each point a different way. A bacterium lifts the neutrophils, a virus the lymphocytes, an allergy the eosinophils and an inflammation that has been running a while the monocytes. Two people with the same total can thus have something quite different. The differential, the count per type, is usually on the same report and is half the story.
What does it mean if my white cells stay low after an infection?
Usually that the bone marrow is still recovering. A virus slows production for a few days and draws cells into the tissue, and the total then stays low for up to a few weeks, without your immune system falling short. Measure again after four weeks; if the count is then back within the band, there is nothing more to do with it.
Which tests include leukocytes?
Leukocytes is in the Biological age test (€69, also as an add-on for €15), in the comprehensive test (€229) and in .
Related biomarkers
Sources
- 1.Unilabs, test catalogue (Dutch): leukocytes. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): leukocytes. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): leukocytes. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): leukocytes. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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