Differential Diagnosis and Workup of Monocytosis: A Systematic Approach to a Common Hematologic Finding

Curr Hematol Malig Rep. 2021 Jun;16(3):267-275. doi: 10.1007/s11899-021-00618-4. Epub 2021 Apr 20.


Purpose of review: Monocytosis is a frequently encountered clinical condition that needs appropriate investigation due to a broad range of differential diagnoses. This review is meant to summarize the latest literature in the diagnostic testing and interpretation and offer a stepwise diagnostic approach for a patient presenting with monocytosis.

Recent findings: Basic studies have highlighted the phenotypic and functional heterogeneity in the monocyte compartment. Studies, both translational and clinical, have provided insights into why monocytosis occurs and how to distinguish the different etiologies. Flow cytometry studies have illustrated that monocyte repartitioning can distinguish chronic myelomonocytic leukemia, a prototypical neoplasm with monocytosis from other reactive or neoplastic causes. In summary, we provide an algorithmic approach to the diagnosis of a patient presenting with monocytosis and expect this document to serve as a reference guide for clinicians.

Keywords: Chronic Myelomonocytic Leukemia; Classical; Intermediate; Monocytes; Monocytosis; Non-classical.

Publication types

  • Review

MeSH terms

  • Biomarkers, Tumor
  • Bone Marrow / pathology
  • Clonal Evolution / genetics
  • Clonal Evolution / immunology
  • Diagnosis, Differential
  • Disease Management
  • Disease Susceptibility
  • Flow Cytometry
  • Humans
  • Leukemia, Myeloid / diagnosis*
  • Leukemia, Myeloid / etiology
  • Leukemia, Myeloid / therapy
  • Leukemia, Myelomonocytic, Chronic


  • Biomarkers, Tumor