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Monocytes are produced in the bone marrow and have the property of leaving the bloodstream and heading for the area of infection. They are able to ingest and destroy bacteria. Monocytes are associated more often with chronic infections than with acute infections. Monocytes are also involved in tissue repair and other immune system functions. The test provides the number of monocytes per litre of blood (monocyte number (#)) and the proportion of white blood cells represented by monocytes (monocyte ratio). Results must be interpreted in light of clinical observations, other results from the current blood count, and variations in results over time.

A high number and/or ratio of monocytes (monocytosis) is found in chronic infections (tuberculosis, fungal infections), heart tissue infections (bacterial endocarditis), certain diseases affecting the blood vessel lining (lupus, scleroderma, rheumatoid arthritis, vasculitis), inflammatory diseases of the digestive tract (Crohn’s disease), and monocytic and myelomonocytic leukemia.

An occasional result showing a reduced number or ratio of monocytes is usually of little clinical significance. If the result is repeated over time, it may indicate bone marrow damage or deficiency or a rare form of leukemia (hairy cell leukemia).

Term of the Week

Hot zone

A hot zone is a section of a facility (sometimes an entire facility or even a city district) where there is a high risk of contamination by patients with an infectious disease. All individuals entering a hot zone must respect appropriate protective measures. By analogy, “cold zone” and “warm zone” are used to refer to areas where there is no infected individual or only individuals suspected of having an infection.