What are monocytes?
After the first wave of neutrophils comes the second: monocytes. They are the largest white blood cells, and in your blood they are in transit. After about three days they crawl through the vessel wall into the tissue and change there into macrophages, literally big eaters, which digest dead cells, bacteria and debris and release signal substances that set repair in motion. Every organ has its own macrophages: in the lungs, the liver, the brain and the vessel wall, and they are replenished from the blood. Because monocytes are only needed after the first wave, the count in your blood rises later than the neutrophils and the CRP. It rises in the recovery phase of an infection, when clearing up is needed, and it stays high as long as an inflammation continues: with a bowel inflammation, rheumatoid arthritis, an infection that persists such as tuberculosis or an infected heart valve. Prednisone and chemotherapy suppress the count. Your report shows the count in ×10⁹/L, and read it as an absolute count, not as a percentage. Normal is about 0.3 to 0.9 ×10⁹/L, where the labs overlap. The lower end says little: monocytes are scarce, and a low count is almost never a finding on its own.
Why are monocytes relevant?
Monocytes tell which phase an inflammation is in. With a fresh bacterial infection the neutrophils are high and the monocytes still normal; a week later, when you feel better, the neutrophils are back and the monocytes rise, because clearing up is under way. A count that stays high while CRP is already falling is therefore no reason for concern but the sign of recovery. A count that stays high together with CRP points to an inflammation that does not stop, and then the question is where it sits. For anyone who is healthy, monocytes are interesting because they are the cell that builds atherosclerosis. Macrophages in the vessel wall swallow LDL particles that have lodged there, fill up with fat and become foam cells, the core of a plaque. More monocytes in your blood means more supply for that process, and a higher count within the band therefore goes with more cardiovascular disease. Smoking and belly fat lift the count persistently, exactly the two things that also strain the vessel wall, and after stopping smoking and losing belly fat the count falls over months. The rare side is a count that stays far above the band without an infection or inflammation. That can be a bone marrow disease, in which the production of monocytes goes astray, and then you usually see abnormalities in the other cells too. That is the reason a persistently high count is checked, even when you feel well.
Monocytes reference ranges
What counts beside the number:
- The absolute count, not the percentage, because that also rises when the neutrophils fall
- CRP from the same draw: high monocytes with a falling CRP is recovery, with a high CRP an inflammation that continues
- Whether you were ill in the weeks before
- Whether you smoke, how much belly fat you carry and whether you have a chronic inflammation, in the gut, the joints or the gums
- Whether you take prednisone, which suppresses the count
- With a count that stays far above the band: the other cells of the blood count
Read monocytes as an absolute count, not as a percentage, because a percentage also rises when the neutrophils fall. A low count rarely means anything on its own; it is the upper end that says something, and then CRP counts alongside: if that is already falling, a high count is the recovery phase. Anyone who smokes sits persistently higher in the band.
What Dutch labs actually use
The floor differs by a factor of three here: 0.1 at Unilabs and Clinical Diagnostics, 0.2 at Star-shl, 0.3 at Certe. Someone at 0.25 is therefore normal at three labs and too low at Certe. On the ceiling they nearly agree: three put it at 1.0 and Certe at 0.9.
0.3 – 0.9×10⁹/L
Between 0.1 and 0.3 and between 0.9 and 1.0 it depends on the lab, because each sets its limits on its own method and population. Above 1.0 every lab calls it abnormal.
every lab calls 0.3 – 0.9 ×10⁹/L normal. Between 0.1 and 0.3 and between 0.9 and 1.0 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Above 15 yrs | 0.1–1.0 ×10⁹/L |
| Star-shl2026 | All ages | 0.2–1.0 ×10⁹/L |
| Certe2026 | Women from 18 yrs | 0.3–0.9 ×10⁹/L |
| Men from 18 yrs | 0.3–0.9 ×10⁹/L | |
| Clinical Diagnostics2026 | From 1 month | 0.1–1.0 ×10⁹/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Monocytes high or low: what it means
A low count almost never means anything on its own. The band starts low, and a count just below it comes from prednisone, chemotherapy or a severe acute infection in which the cells have been drawn en masse into the tissue. As soon as the cause is gone, the count comes back. Only a low count beside low neutrophils, anaemia and few platelets says something about the bone marrow as a whole. A high count means clearing up is under way, and the question is whether that is a phase or a state. Usually it is the first and rarely the last: the recovery phase after an infection, with CRP already falling; an inflammation that has been running a while, such as a bowel inflammation or rheumatoid arthritis; an infection that persists; smoking; and an autoimmune disease. A count that repeatedly stays far above the band without one of those explanations, and certainly with abnormalities in the other cells, should have the bone marrow looked at. Always read the absolute count: when the neutrophils fall, the percentage of monocytes rises without a single cell having been added. What you do about it: with a rise in the recovery phase nothing but letting it pass, and measuring again after a few weeks. With a count that stays at the high end without an infection, stopping smoking is the biggest step, and after that less belly fat, because those two keep the cleaners permanently at work. Regular exercise and a diet with plenty of fibre and little processed food suppress the smouldering inflammation monocytes respond to. Tackling a chronic inflammation, in the gut, the joints or the gums, lets the count fall along. Monocytes belongs beside CRP, which says whether the inflammation is still active or already dying down, beside the neutrophils and lymphocytes, which show the phase of an infection, and beside the total of white cells.
What lowers it
Rarely a finding on its own; the cells are temporarily suppressed or drawn into the tissue.
| Cause | How often |
|---|---|
| CorticosteroidsPrednisone suppresses the count during a course; afterwards it comes back | Often |
| ChemotherapyDrugs that slow cell division hit the production of monocytes too; the count recovers after treatment | Sometimes |
| Severe acute infectionThe cells have been drawn en masse into the tissue; in the recovery phase the count comes back and often overshoots briefly | Rare |
What raises it
Clearing up is under way, and the question is whether that is a phase or a state.
| Cause | How often |
|---|---|
| Recovery after an infectionThe cleaners come after the first wave; the count rises while CRP is already falling, and is back after a few weeks | Often |
| Longer-standing inflammationA bowel inflammation, rheumatoid arthritis or inflamed gums keep the cleaners at work as long as the inflammation continues | Often |
| An infection that persistsTuberculosis, an infected heart valve or an abscess that does not heal; then CRP stays high too | Sometimes |
| SmokingKeeps the lungs in a light inflammatory state and lifts the count persistently; after stopping it falls over months | Sometimes |
| Autoimmune diseaseLupus or sarcoidosis, in which the immune system attacks the body's own tissue and the cleaners are permanently at work | Sometimes |
| Bone marrow diseaseWith a count that stays far above the band without an infection, with abnormalities in the other cells, production itself goes astray | Rare |
How does a monocytes blood test work?
- Referral
- Not needed. Monocytes are in every blood count with differential, and you can have that measured yourself.
- Fasting
- Not needed; the count does not respond to food or to the time of day.
- When
- Not in the weeks after an infection if you want to know your usual level, because in the recovery phase the count sits higher. If you want to see whether an inflammation is dying down, measure beside CRP.
- The draw
- One tube of blood from a vein in your arm. The lab counts the white cells and sorts them into five types; CRP can come from the same draw.
- Repeating
- With a high count after four to six weeks, when you are well, to see whether it was the recovery phase. Otherwise once a year.
- Which test
- Monocytes 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 monocytes?
The cleaners of your immune system, and the largest white blood cells. They circulate in your blood for a few days, then crawl into the tissue and become macrophages there: cells that digest dead cells, bacteria and debris and release signal substances that set repair in motion. Every organ has its own macrophages, and they are replenished from the blood.
What is a normal monocyte value?
Between 0.3 and 0.9 ×10⁹/L, where the four labs overlap. A non-smoker usually sits in the lower half. Read the absolute count, not the percentage, because that also rises when the neutrophils fall without a single monocyte having been added. And do not measure in the weeks after an infection, because then the count naturally sits higher.
What does a high monocyte count mean?
That clearing up is under way. Usually it is the recovery phase after an infection: the cleaners come after the first wave, and the count rises while CRP is already falling. If the count stays high with a high CRP alongside, an inflammation is continuing, such as a bowel inflammation, rheumatoid arthritis or an infection that persists. Smoking and belly fat keep the count persistently high. A count that stays far above the band without explanation is checked.
What does a low monocyte count mean?
Almost never anything on its own. Monocytes are scarce, and a count just below the band comes from prednisone, chemotherapy or a severe acute infection in which the cells have been drawn into the tissue. As soon as the cause is gone, the count comes back. Only a low count beside low neutrophils, anaemia and few platelets says something about the bone marrow as a whole.
Why do my monocytes rise when I am already getting better?
Because the cleaners only get their turn after the first wave. With a fresh infection the neutrophils are high and the monocytes still normal; a week later, when you feel better, the neutrophils are back and the monocytes rise to digest dead cells and debris. A high count with a falling CRP is therefore the sign of recovery, and it is back by itself after a few weeks.
What do monocytes have to do with atherosclerosis?
They are the cell that builds the plaque. Macrophages in the vessel wall swallow LDL particles that have lodged there, fill up with fat and become foam cells, the core of a plaque. More monocytes in your blood means more supply for that process. That is why a higher count within the band goes with more cardiovascular disease, and why smoking and belly fat, which lift the count, count double.
How do I bring my monocytes down?
In the recovery phase you need do nothing; the count falls by itself. If it stays at the high end without an infection, stopping smoking is the biggest step, and after that less belly fat, because those two keep the cleaners permanently at work. Regular exercise and eating with plenty of fibre and little processed food suppress the smouldering inflammation. Tackling a chronic inflammation in the gut, the joints or the gums lets the count fall along.
When is a high count checked?
When it repeatedly stays far above the band without an infection, inflammation or smoking as explanation, and certainly when there are also abnormalities in the other cells of the blood count. Then the production of monocytes itself may have gone astray, and that is looked at in the bone marrow. That is rare, but it is the reason a persistently high count is not waved away, even when you feel well.
Which tests include monocytes?
Monocytes 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): white cell differential. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): monocytes. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): monocytes. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): monocytes. 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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