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Monocytes (Percent)

The share of your white blood cells that are monocytes. The absolute monocyte count is usually the more useful number.

AI-verified against cited sources. Awaiting expert reviewAlso called Mono%, MONO%LOINC 5905-5

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What it is

Monocytes are white blood cells that clear away germs and dead cells and help direct the immune response. On a CBC with differential, the lab sorts your white cells into types and reports each as a percent of the total. This line is the monocyte share. Because all the types add up to 100, the percent can move when a different white cell type goes up or down, even if the number of monocytes has not changed.

Why it matters

A monocyte percent that is high or low is a clue, not an answer. It can reflect an infection, inflammation or recovery from illness, but it can also shift only because another white cell type changed. Clinicians pair it with the absolute monocyte count and your total white blood cell count to see what is really happening.

If it’s low

A low monocyte percent usually means another cell type has taken a bigger share, for example neutrophils during a bacterial infection or lymphocytes during a viral illness. It can also mean there are fewer monocytes, so check the absolute count.

Common causes

  • A rise in another white cell type, such as neutrophils or lymphocytes
  • Corticosteroid (steroid) medicines
  • Acute illness, including viral infections such as Epstein-Barr virus
  • Treatments or conditions that lower several blood counts, such as chemotherapy

What can help

  • Ask your clinician to review the absolute monocyte count, which shows whether the number of monocytes is actually low
  • Ask whether to repeat the test after an illness or after treatment ends

If it’s high

A high monocyte percent means monocytes make up a larger share of your white cells than usual. That can happen when monocytes rise, or when other white cells such as neutrophils or lymphocytes are low. Check the absolute count to see which it is. Many harmless and short-lived things can cause it.

Common causes

  • Recovery from an infection or from a temporary drop in blood counts
  • Viral infections such as mononucleosis, mumps or measles
  • Longer-lasting infections such as tuberculosis or parasite infections
  • Chronic inflammatory conditions
  • Low counts of other white cells, which leave monocytes with a bigger share
  • Less often, a blood or bone marrow condition

What can help

  • Ask your clinician to look at the absolute monocyte count and your total white blood cell count alongside the percent
  • Ask whether to repeat the test after a recent illness has passed

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 4.1–12.4 %. Source: ARUP Laboratories, Labcorp, Quest Diagnostics, MedlinePlus, National Library of Medicine.

See Monocytes % by age and sex, with the U.S. survey numbers where they exist.

How common is your level?

NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.

How Monocytes % varies with age in the U.S.Shaded: middle 90% and middle 50% of people. Line: the median. %. Point at any age, or focus the chart and use the arrow keys, to read both sexes in words.

Use the left and right arrow keys to read each age. Shift moves five years.

Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.

Explore Monocytes % by age and sex: every percentile as a table, with a download.

What can affect your result

  • All the other white cell types, since the percentages add up to 100
  • Recent or ongoing infection and recovery from illness
  • Inflammation or autoimmune conditions
  • Medicines such as steroids (can lower) and growth-factor injections (can raise)
  • Age: babies and young children have different usual percentages than adults
  • Lab method: published adult ranges differ by lab
  • The percent moves when any other white cell type rises or falls, because all the percentages add up to 100.
  • Recent or ongoing infection, and recovery from illness, can raise monocytes.
  • Corticosteroid medicines can lower monocytes. Growth-factor injections (G-CSF) can raise them.
  • Large lymphocytes and young cells can be hard for analyzers to tell from monocytes, so the lab may review a blood smear under the microscope.
  • A difficult draw, a clotted sample or a sample that is too old can throw off cell counts.

Can change within days as an infection or inflammation comes and goes.

When to talk to a clinician

A monocyte percent by itself rarely needs urgent attention. Ask your clinician to look at the absolute monocyte count and your other results. Talk with a clinician if a high or low result comes with fever, night sweats, unexplained weight loss or frequent infections. If you feel very unwell, call 911 or your local emergency number.

Questions you could ask

  • Which of my results matter most on this differential?
  • Is the range on my lab report the right one for me?
  • Is my absolute monocyte count also high?
  • Could a recent infection or inflammation explain this?
  • Is my absolute monocyte count low, or is another white cell type taking a bigger share?
  • Should we repeat the test after I have recovered from any illness?

Questions people ask

Why does my lab not show a range for monocyte percent?

Some labs, including Labcorp on its CBC with differential, give a range only for the absolute counts and print 'Not Estab.' for the percentages. Percentages depend on every other white cell type, so the absolute counts are easier to interpret.

Can my monocyte percent be high when the absolute count is in the usual range?

Yes. If your neutrophils or lymphocytes are low, monocytes make up a bigger share of a smaller total, so the percent can look high while the actual number is unchanged. The absolute count shows which is true.

What monocyte percent is typical?

Published figures vary. ARUP's adult interval is 4.1% to 12.4%, and MedlinePlus lists 2% to 8%. Your own lab's range, when it prints one, is the one to use.

Show the science and sources

Units

  • 1 % = 1 %
  • 1 % = 0.01 fraction (0–1)

Open the Monocytes % unit converter

For clinicians and researchers

Relative monocytes are reported as a percent of total leukocytes by automated 5-part analyzers, or counted on a manual differential. The differential is a closed system, so an increase in one cell line lowers the percentages of the others, and the absolute monocyte count should guide interpretation. ARUP's adult interval is 4.1%–12.4%, MedlinePlus lists 2%–8%, and Labcorp does not establish a percent interval for adults and prints 'Not Estab.'.

LOINC 5905-5 (primary), 26485-3, 744-3, 71677-9. Specimen: whole-blood.

Sources

  1. CBC with Platelet Count and Automated Differential (test 0040003), hotline effective March 1, 2021, ARUP Laboratories (2021)
  2. CBC With Differential/Platelet, sample patient report (test 005009), Labcorp
  3. CBC (includes Differential and Platelets) (test code 6399), Quest Diagnostics
  4. Blood differential test, MedlinePlus, National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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