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Causes of high and low monocyte counts
Last reviewed: 04.07.2025
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Monocytosis - an increase in the number of monocytes in the blood of more than 0.8×10 9 /l - accompanies a number of diseases. Monocytes are elevated in tuberculosis; the occurrence of monocytosis is considered evidence of the active spread of the tuberculosis process. An important indicator is the ratio of the absolute number of monocytes to lymphocytes, which is normally 0.3-1.0. This ratio is more than 1 in the active phase of the disease and decreases during recovery, which is used to assess the course of tuberculosis.
Diseases and conditions in which monocytosis is possible
Main reasons |
Clinical forms |
| Infections | Subacute infective endocarditis; convalescence after acute infections; viral ( infectious mononucleosis ), fungal, rickettsial and protozoal infections ( malaria, leishmaniasis ) |
| Granulomatosis | Tuberculosis, especially active; syphilis; brucellosis; sarcoidosis; ulcerative colitis |
| Blood diseases | Acute monoblastic and myelomonoblastic leukemia; chronic monocytic, myelomonocytic and myeloleukemia; lymphogranulomatosis |
Collagenoses |
Systemic lupus erythematosus, rheumatoid arthritis, polyarteritis nodosa |
Also, monocytes are elevated in infective endocarditis, sluggish sepsis, which is often observed in the absence of leukocytosis. Relative or absolute monocytosis is noted in 50% of patients with systemic vasculitis. Short-term monocytosis can develop in patients with acute infections during the convalescence period.
Monocytopenia is a decrease in the number of monocytes to less than 0.09×10 9 /l. Monocytes are reduced in hematopoietic hypoplasia.