Monocytes are cells that work in our immune system and thus belong to the white blood cell family. Lymphocytes, neutrophils, monocytes, eosinophils, and basophils levels are assessed through a blood differential test (also called a white blood cell differential) as a part of a complete blood count. This test can detect abnormal or immature cells and can diagnose an infection, leukemia, or an immune disorder. A healthcare professional may order a blood differential when someone has general signs and symptoms of infection and/or inflammation, such as:
- Fever, chills
- Body aches, pains
Monocytes are a large type of white blood cell but only account for 2%-8% of the total white blood cells in circulation. Once in the blood, monocytes migrate to tissues where they mature into macrophages. Similar in function to neutrophils, macrophages are scavenger cells of the immune system, serving to remove dead/damaged cells or destroy invasive microorganisms.
Low monocyte count, called monocytopenia, is caused by anything that decreases the overall white blood cell count, such as:
- A severe infection, such as sepsis, which is wiping out white blood cells faster than the body can make them
- Diseases affecting the bone marrow, like lupus and HIV
- Medications that impact the bone marrow (e.g., chemotherapy)
High monocyte count, called monocytosis, occurs with:
- Chronic infections
- Chronic inflammatory disease
- Certain cancers, like Myelomonocytic leukemia
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