Monocytes in a blood test: normal range and results (MON)
The source gives the result as a percentage of the whole white cell count (the white cell differential); the absolute amount ×10⁹/l is calculated from the total white cell count and stated on the laboratory report
- Updated
- 2026-09-30
- Every number with its source
What monocytes are
Monocytes are one of the five types of white blood cell (leukocyte), alongside neutrophils, lymphocytes, eosinophils and basophils. They are made in the bone marrow and circulate in the blood only briefly, after which they move into the tissues, where they turn into macrophages or dendritic cells — cells that “devour” bacteria, dead cells and other foreign particles, and that activate other parts of the immune system. The amount of monocytes is determined by a blood differential test (the white cell differential), which is most often ordered together with a full blood count. The result is usually given as a percentage of the whole white cell count, while the absolute monocyte number (×10⁹/l) is calculated from the total white cell count and stated on the laboratory report. Changes in the amount of monocytes are rarely used for a diagnosis in themselves — a doctor assesses them together with the other values of the white cell differential, the full blood count and the clinical symptoms.
The reference range for monocytes
| Group | Range, % | Source |
|---|---|---|
| Adults The source gives the result as a percentage of the whole white cell count (the white cell differential); the absolute amount ×10⁹/l is calculated from the total white cell count and stated on the laboratory report | 2–8 | MedlinePlus Reviewed 2025-02-03 |
When monocytes are tested
- As part of a full blood count with a white cell differential (a blood differential test) during a preventive check-up
- When an infection is suspected, in order to establish its cause or its nature
- When monitoring an already known disease of the blood, or a condition related to it
- When feeling unusually tired or weak, or after noticing unexplained bruises or other unusual symptoms
- When assessing the effect of treatment that acts on blood formation or the immune system
How to prepare
- No special preparation is needed (MedlinePlus)
- If the test is taken together with other blood tests (for example glucose or a lipid panel), follow the requirements for those tests, which your doctor or the laboratory will tell you about
A raised monocyte count
A raised monocyte percentage is considered a deviation according to the MedlinePlus blood differential test guidance (the range is 2–8 %). Possible causes include chronic inflammatory diseases, infections (including tuberculosis and viral infections such as infectious mononucleosis, mumps or measles) and diseases of the blood such as leukaemia. The cause is easier to establish when the other values of the white cell differential and the clinical picture are assessed alongside.
- A chronic inflammatory disease
- Leukaemia or another disease of the blood
- A parasitic infection
- Tuberculosis (a bacterial infection involving the lungs)
- A viral infection — for example infectious mononucleosis, mumps or measles
- Crohn's disease and sarcoidosis — examples of chronic inflammatory diseases that the Danish physicians' handbook Lægehåndbogen links with monocytosis
- Some malignant diseases — Hodgkin's disease, monocytic leukaemia and chronic myeloid leukaemia (according to Lægehåndbogen)
What is usually assessed alongside a raised result:
- A full blood count and the complete white cell differential — whether other types of white blood cell deviate as well
- Inflammatory markers (CRP, ESR), if a chronic inflammatory disease is suspected
- Symptoms and any recent infections that could have affected the result
- Whether the test needs to be repeated, in order to assess the change over time
A reduced monocyte count (monocytopenia)
A reduced monocyte count is called monocytopenia: the Merck Manual defines it as a monocyte count in the blood below 200/µl (0.2 ×10⁹/l). Possible causes include chemotherapy or other treatment that suppresses the bone marrow, treatment with corticosteroids, a severe infection, diseases of the bone marrow (for example aplastic anaemia or hairy cell leukaemia) and a rare inherited GATA2 deficiency. A doctor assesses the result together with the whole white cell differential.
- Chemotherapy or other treatment that suppresses the bone marrow
- Treatment with corticosteroids or immunoglobulins
- A severe infection, including a bloodstream infection
- Diseases of the bone marrow — aplastic anaemia, some leukaemias (for example hairy cell leukaemia)
- A rare inherited GATA2 deficiency, in which some lymphocytes are also reduced
What is usually assessed alongside a reduced result:
- Whether other white blood cells — neutrophils, lymphocytes — or the total white cell count are reduced as well
- Medicines being taken, especially corticosteroids, and any recent treatment that acts on the bone marrow
- A recent or ongoing infection
- Whether the test needs to be repeated, to see whether the change persists
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Frequently asked questions
›What is the normal monocyte count in blood?
According to the MedlinePlus blood differential test, in adults monocytes make up 2–8 % of the whole white blood cell (leukocyte) count. You will find the exact laboratory interval, and also the absolute amount ×10⁹/l, on your own report, because it depends on the method used. The laboratory of Bornholm Hospital in Denmark, for example, assesses the absolute monocyte count in adults (from 18) against an interval of 0.2–0.8 ×10⁹/l.
›What do raised monocytes mean?
A raised monocyte percentage, according to MedlinePlus, can be linked to a chronic inflammatory disease, an infection (including tuberculosis or viral infections such as infectious mononucleosis), a parasitic infection, or diseases of the blood such as leukaemia. The result should be discussed with a doctor together with your other tests.
›What does a low monocyte count mean?
A reduced monocyte count is called monocytopenia. The Merck Manual states that it can be caused by chemotherapy, treatment with corticosteroids, a severe infection, diseases of the bone marrow or a rare inherited GATA2 deficiency. A single lower result says nothing on its own — a doctor looks at whether other white blood cells are reduced as well and whether the change persists.
›What is the function of monocytes in the body?
Monocytes are a type of white blood cell that circulates in the blood only briefly and later moves into the tissues and turns into macrophages or dendritic cells — they “devour” bacteria and dead cells and help activate other parts of the immune system.
›Is any special preparation needed before a monocyte test?
No, according to MedlinePlus no special preparation is needed. If the test is taken together with other blood tests, you may need to follow the requirements for those tests — your doctor or the laboratory will tell you about that.
›When is a monocyte (white cell differential) test done?
The test is most often done together with a full blood count — during a preventive check-up, when an infection or its cause is suspected, and also when monitoring an already known disease of the blood or assessing the effect of treatment.
›Is the monocyte count assessed separately from the other white blood cells?
No, monocytes are only one of the five types of leukocyte in the white cell differential (alongside neutrophils, lymphocytes, eosinophils and basophils). A doctor always assesses the result together with the whole differential and the full blood count, not in isolation.
Sources
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This site is not an emergency service. If severe chest or head pain, breathlessness, confusion, difficulty speaking, heavy bleeding or another acute problem has come on suddenly — do not wait for tests, call 112.
This information is not a diagnosis and does not replace a consultation with a doctor. Reference ranges depend on the laboratory, your age and sex — always compare your result with the range printed on your own report.