Lab result explainedBlood count (CBC)Last updated November 1, 2026

Monocytes on a blood test: what high and low monocytes mean

Monocytes (MONO) · CBC with differential · reported in ×10³/µL (same as ×10⁹/L); also reported as % of white blood cells

Monocytes are the largest type of white blood cell, made in the bone marrow and sent into the blood for a day or two before they move into tissues and turn into macrophages, the cells that engulf germs, clear dead cells and help switch inflammation on and off. On a CBC with differential, most US labs call 0.2–0.8 ×10³/µL (200–800 cells per microlitre), or about 2–8% of all white cells, normal for adults. The two most common reasons the number is off are a recent or ongoing infection, which pushes it up as the marrow responds, and the normal recovery phase after a viral illness or a course of chemotherapy, when it can dip or spike for a few weeks.

A mildly raised monocyte count is one of the most frequent incidental findings on a blood count, and on its own it is rarely the first sign of anything serious. It is a non-specific marker: it tells a clinician the innate immune system is busy, not why. Chronic infections such as tuberculosis, autoimmune disease, smoking and recovery from an acute infection all raise it. A persistently high count (over 1.0 ×10³/µL for more than three months) with no explanation is what justifies a closer look at the marrow.

This page explains how the number is derived, what the percentage and the absolute count each tell you, the real causes of high and low monocytes in order of how often they turn up, which other markers a clinician reads it beside, and what usually happens next.

MONO at a glance

Monocytes are white blood cells that become tissue macrophages; they clear germs, debris and dead cells and help regulate inflammation.
Normal adult range: about 0.2–0.8 ×10³/µL absolute, or 2–8% of white cells (labs vary; some accept up to 1.0 ×10³/µL or 10%).
High monocytes (monocytosis) most often mean infection, recovery from infection, chronic inflammation or smoking; rarely a bone marrow disorder.
Low monocytes (monocytopenia) are usually from steroids, chemotherapy or an acute illness; very low counts that persist need a haematology review.
Read the absolute count, not just the percentage; a high percentage with a normal absolute count usually just reflects low neutrophils or lymphocytes.
Next step: repeat the CBC in 4–6 weeks once you are well; persistent monocytosis above 1.0 ×10³/µL deserves a blood film and a clinician's review.

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What MONO measures

The monocyte result comes from the white cell differential, the part of a complete blood count that sorts white cells into five types: neutrophils, lymphocytes, monocytes, eosinophils and basophils. An automated analyser classifies tens of thousands of cells by size, granularity and how they scatter light, and reports monocytes two ways: as a percentage of all white cells (MONO%) and as an absolute number (ABS MONO or AMC), calculated by multiplying the percentage by the total white cell count.

The absolute count is the number that matters clinically. If your total white count is low because neutrophils are suppressed, monocytes can read as 15% while the absolute count is perfectly normal. Conversely, in a strong infection the percentage can look ordinary while the absolute count is high. If the analyser flags unusual cells, a technologist reviews a stained blood film by eye, which is also where immature or abnormal monocytes would be noticed.

Normal range for MONO

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (×10³/µL (same as ×10⁹/L); also reported as % of white blood cells)	Notes
Adults, absolute count	0.2–0.8 ×10³/µL	Some labs use 0.1–1.0 ×10³/µL. Monocytosis is usually defined as more than 0.8–1.0 ×10³/µL.
Adults, percentage	2–8% of white blood cells	Up to 10% on some reports. Always check the absolute count.
Children	0.1–1.2 ×10³/µL (varies by age)	Newborns and infants run higher; paediatric reference ranges apply.
Pregnancy	Similar to adult range	Total white cells rise in pregnancy; monocytes change little, so the percentage may look lower.
Monocytopenia	Below 0.2 ×10³/µL	Below 0.1 ×10³/µL on repeat testing is significant.

High monocytes (monocytosis)

A high monocyte count means the bone marrow is releasing more monocytes, usually in response to infection or inflammation that has been going on for days to weeks rather than hours. Monocytes are slower to rise than neutrophils, so monocytosis often marks the later or chronic phase of an immune response, or the recovery phase after an acute one.

Mild monocytosis (0.8–1.5 ×10³/µL) with an obvious explanation and an otherwise normal blood count is almost always reactive and settles on its own. What raises concern is a count that stays above 1.0 ×10³/µL for three months or more, makes up more than 10% of white cells, or comes with anaemia, low platelets, an enlarged spleen or abnormal cells on the film. That pattern needs a haematologist to rule out chronic myelomonocytic leukaemia (CMML) or another marrow disorder.

Common causes

Recovery from an acute infection
As a bacterial or viral infection resolves, monocytes rise for one to three weeks to clear debris and repair tissue. This is the single most common reason for a mildly high result and needs no treatment.
Chronic or lingering infection
Tuberculosis, infective endocarditis, syphilis, brucellosis and some fungal and parasitic infections stimulate monocyte production over weeks. Mononucleosis (EBV) and CMV also raise monocytes alongside lymphocytes.
Smoking
Smokers run higher total white cells, including monocytes, from ongoing airway inflammation. Counts fall over months after quitting.
Autoimmune and inflammatory disease
Rheumatoid arthritis, lupus, inflammatory bowel disease, sarcoidosis and vasculitis drive monocyte release through inflammatory cytokines such as GM-CSF and IL-6. The count tends to track disease activity.
Obesity and metabolic inflammation
Excess visceral fat produces a low-grade inflammatory signal that modestly raises monocyte counts and shifts them toward an inflammatory subtype. The rise is usually within or just above the reference range.
Medications
Corticosteroids can transiently raise monocytes, and G-CSF or GM-CSF (filgrastim, sargramostim) given after chemotherapy reliably do. Lithium raises white cells generally. Olanzapine and clozapine occasionally cause monocytosis.
Asplenia (no spleen)
Without a spleen to filter cells, circulating monocytes stay higher. The same is true after splenectomy for any reason.
Chronic myelomonocytic leukaemia (CMML) and other marrow disorders
CMML is defined by a monocyte count above 1.0 ×10³/µL and above 10% of white cells persisting for over three months with no other explanation. Myelodysplastic syndromes, chronic myeloid leukaemia and some acute leukaemias can also present with monocytosis, usually with other abnormalities on the count.
Lymphoma, Hodgkin disease and some solid cancers
Tumours release cytokines that stimulate monocyte production, so a persistently high count with weight loss, night sweats or enlarged nodes should be investigated.
Lab timing effects
Monocyte counts have a mild daily rhythm and rise slightly after intense exercise. Neither explains a count well above 1.0 ×10³/µL.

Symptoms that can go with it

Often none; the result is found incidentally
Lingering tiredness, low-grade fever or night sweats if an infection or inflammatory process is behind it
Joint pain, rash, mouth ulcers or gut symptoms in autoimmune disease
Cough, weight loss and sweats in tuberculosis
Fullness under the left ribs (enlarged spleen), easy bruising or breathlessness when a marrow disorder is the cause

Low monocytes (monocytopenia)

A low monocyte count usually means the marrow is temporarily making fewer white cells or that monocytes have been pulled out of the blood into tissues. Isolated, mild monocytopenia is common and often a lab snapshot: a count of 0.1–0.2 ×10³/µL that is normal on repeat means nothing.

Because a normal count is already small, the result is only meaningful when it is consistently near zero or when it travels with low neutrophils and low lymphocytes, which points to marrow suppression or failure. A persistently absent monocyte count with recurrent unusual infections (mycobacteria, warts, fungal infections) is the clue to rare inherited GATA2 deficiency, sometimes called MonoMAC syndrome.

Common causes

Corticosteroids
Prednisone and similar drugs cause a fall in monocytes within hours of a dose, with recovery after the course ends. This is the most common drug cause.
Chemotherapy and radiotherapy
Marrow suppression lowers all white cells; monocytes are often the first to fall and the first to recover, so their return is used as an early sign the marrow is bouncing back.
Acute severe infection or sepsis
In overwhelming infection monocytes leave the blood for tissues faster than they are replaced, and endotoxin can suppress their release. The count typically rebounds as the infection is controlled.
Hairy cell leukaemia
This rare, slow-growing leukaemia characteristically causes marked monocytopenia together with low neutrophils and an enlarged spleen. It is one reason a persistently absent monocyte count gets a specialist review.
Aplastic anaemia and marrow failure
When the marrow stops producing cells, monocytes fall alongside red cells, platelets and neutrophils. The pattern on the full count, not the monocyte number alone, makes the diagnosis.
HIV and other immune disorders
Advanced HIV, severe vitamin B12 or folate deficiency and some autoimmune conditions reduce monocyte production.
GATA2 deficiency (MonoMAC syndrome)
A rare inherited condition in which monocytes, B cells and NK cells are nearly absent, leading to mycobacterial, fungal and HPV infections and a high risk of myelodysplasia. It is diagnosed by genetic testing.
Interferon and some biologic drugs
Interferon-alpha, some TNF inhibitors and immunosuppressants used after transplant can lower monocytes.

Symptoms that can go with it

Usually none when mild or transient
Recurrent or unusual infections (mycobacterial, fungal, persistent warts) when the count is persistently absent
Fatigue, bruising, pallor or frequent fevers if it is part of general marrow suppression
An enlarged spleen or abdominal fullness in hairy cell leukaemia

Read it alongside

Total white blood cell count — the absolute monocyte count is percentage × WBC; a high percentage with a low WBC is a different problem from true monocytosis.
Neutrophils — together they separate a reactive response (both up in bacterial infection) from an isolated monocyte problem.
Lymphocytes — raised monocytes plus atypical lymphocytes points to a viral cause such as EBV or CMV.
Hemoglobin and platelets — anaemia or low platelets with monocytosis raises the possibility of a marrow disorder and prompts a blood film.
CRP — a high CRP confirms active inflammation or infection as the likely driver; a normal CRP with persistent monocytosis is more unusual.
Blood film (peripheral smear) — the single most useful next test, showing whether the monocytes look mature and whether immature cells are present.

What usually happens next

If you were recently ill, had surgery or are on steroids, repeat the CBC with differential in 4–6 weeks once you are well; most results normalise.
Ask your clinician to look at the absolute count and the rest of the differential, not just the percentage flagged in red.
If the count stays above 1.0 ×10³/µL or above 10% on repeat, a peripheral blood film, CRP, liver and kidney tests, and tests for chronic infection (TB screen, HIV, EBV) are the usual next layer.
Mention night sweats, unexplained weight loss, enlarged lymph nodes, bruising, or fullness under the left ribs; these change the urgency.
Monocytosis that persists for more than three months with no cause, or that comes with anaemia or low platelets, is referred to haematology, where a marrow biopsy may be considered.

Diet, lifestyle and natural levers with evidence

What can move MONO once the cause is known. Nothing here replaces finding the cause.

Stop smoking

Strong evidence

In the EPIC-Norfolk study of over 20,000 adults, current smokers had higher total white cell counts, including monocytes, than never-smokers, with counts falling progressively in ex-smokers over years since quitting. Quitting is the single most reliable lifestyle change for a mildly raised count with no other cause.

Regular moderate exercise

Moderate evidence

A 12-week exercise training programme in older adults cut the proportion of inflammatory CD14+CD16+ monocytes and lowered monocyte TNF-alpha production. Regular aerobic activity lowers resting inflammatory tone; a single hard session temporarily raises counts for a few hours, so avoid testing straight after training.

Weight loss and a Mediterranean-style diet

Moderate evidence

Weight-loss trials in people with obesity show reductions in circulating inflammatory monocytes and in CRP; Mediterranean-diet trials such as PREDIMED reduced inflammatory markers in high-risk adults. The effect on the monocyte count itself is modest and sits within the normal range.

Omega-3 fatty acids (EPA and DHA)

Preliminary evidence

Small trials show fish-oil supplementation (around 2–4 g/day of EPA+DHA) reduces monocyte production of inflammatory cytokines and tissue factor, and may lower the inflammatory monocyte subset. No trial has used the monocyte count as its main outcome.

Doses above 3 g/day can increase bleeding tendency; check with a clinician if you take anticoagulants.

Correct vitamin B12 and folate deficiency

Moderate evidence

Severe B12 or folate deficiency suppresses all marrow cell lines, and replacement restores normal counts within weeks. This applies to low monocytes with a documented deficiency; it does not apply to high monocytes and should not be taken without a measured low level.

Test first. Supplementing without a deficiency does nothing for the count and can mask the cause.

When to see a clinician promptly

Monocytes above 1.5 ×10³/µL, or any monocytosis with anaemia, low platelets, or abnormal cells reported on the film.
A high count that persists beyond three months with no explanation, or that keeps rising on repeat tests.
Night sweats, unexplained weight loss of more than 5% in six months, persistent fever, enlarged lymph nodes or a swollen spleen.
A persistently very low or absent monocyte count with unusual or repeated infections.
Any new count abnormality while on chemotherapy, immunosuppressants or clozapine, which need a same-day call to the prescribing team.

Frequently asked questions

Is a monocyte count of 1.0 bad?

A count of 1.0 ×10³/µL is at the upper edge of normal on many reports and mildly high on others. On its own, especially after an infection, it is usually reactive and settles. It becomes a concern if it stays at that level for three months or more, makes up over 10% of white cells, or comes with anaemia, low platelets or abnormal cells on the film.

What does it mean if my monocyte percentage is high but the absolute count is normal?

It usually means another white cell type is low, so monocytes make up a bigger share of a smaller total. A normal absolute count is reassuring. Look at the neutrophil and lymphocyte numbers to see which one is pulling the percentage up.

Can stress raise monocytes?

Acute physical stress, including intense exercise and surgery, can raise monocytes for a day or two through adrenaline and cortisol effects. Chronic psychological stress has been linked to a shift toward inflammatory monocytes in research studies, but it rarely pushes the count outside the normal range by itself.

What cancers cause high monocytes?

The marrow cancers most associated with monocytosis are chronic myelomonocytic leukaemia (CMML), acute myelomonocytic and monocytic leukaemias, and chronic myeloid leukaemia. Hodgkin lymphoma and some solid tumours can cause reactive monocytosis. In all of these, the count is usually persistently high and other parts of the blood count are also abnormal. Most high monocyte results are not cancer.

Can dehydration affect the monocyte count?

Dehydration concentrates the blood, so all cell counts, including monocytes, read slightly higher. The effect is small, typically a few percent, and would not turn a normal result into a clearly abnormal one.

Do monocytes go up with a viral infection?

Yes. Viral infections such as EBV (mono), CMV, hepatitis and influenza often raise monocytes, particularly in the second and third weeks as the body clears the infection. They are usually accompanied by a rise in lymphocytes, which helps tell a viral picture from a bacterial one.

How long does it take for monocytes to return to normal?

After an uncomplicated infection, the count usually normalises within two to six weeks. After stopping steroids, low counts recover within days. If the count is still abnormal at a repeat test six to eight weeks later, that is the point to look for an ongoing cause.

References

Blood differential test. MedlinePlus, US National Library of MedicineView source
Riley LK, Rupert J. Evaluation of patients with leukocytosis. American Family Physician (2015)View source
Lynch DT, Hall J, Foucar K. How I investigate monocytosis. International Journal of Laboratory Hematology (2018)
Monocytopenia. Merck Manual Professional VersionView source
Vinh DC, Patel SY, Uzel G, et al.. Autosomal dominant and sporadic monocytopenia with susceptibility to mycobacteria, fungi, papillomaviruses, and myelodysplasia. Blood (2010)
Arber DA, Orazi A, Hasserjian R, et al.. The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood (2016)
Smith MR, Kinmonth AL, Luben RN, et al.. Smoking status and differential white cell count in men and women in the EPIC-Norfolk population. Atherosclerosis (2003)
Timmerman KL, Flynn MG, Coen PM, Markofski MM, Pence BD. Exercise training-induced lowering of inflammatory (CD14+CD16+) monocytes: a role in the anti-inflammatory influence of exercise?. Journal of Leukocyte Biology (2008)
Omega-3 fatty acids: fact sheet for health professionals. NIH Office of Dietary SupplementsView source
Blood basics. American Society of HematologyView source

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.