What are the causes of monocytosis in leukocytosis?

Updated: May 19, 2020
  • Author: Susumu Inoue, MD; Chief Editor: Jennifer Reikes Willert, MD  more...
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Monocytosis is defined as a monocyte count that exceeds the upper limit of the reference range of 0.95 X 199/L (950/μL). Monocytosis is commonly caused by the following conditions:

A study by Cherfane et al indicated that a finding of monocytosis, along with a low lymphocyte/monocyte ratio, can identify the presence of active ulcerative colitis, as opposed to ulcerative colitis in remission. According to the investigators, a monocyte count of 483 and a lymphocyte/monocyte ratio of 3.1 had a sensitivity of 60% for active ulcerative colitis, along with a specificity of 61% and 53%, respectively. It was also found that a monocyte count of greater than 860 and a lymphocyte/monocyte ratio of less than 1.6 had a positive predictive value of 75% for active ulcerative colitis. [32]

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