Carla S. Wilson, MD, PhD

The monocyte image has a reniform nucleus with slightly clumped chromatin and abundant pale blue cytoplasm. Unlike the metamyelocyte and neutrophil, no secondary cytoplasmic granulation is observed.

Monocytes image are strongly positive for nonspecific esterase stains, including α-naphthyl butyrate esterase, as shown here. In contrast, neutrophils image show negative staining.



  • Increased monocytes, monocytic hyperplasia


  • Absolute blood monocyte count > 0.8 × 109/L in adults and > 3.5 × 109/L in neonates

  • Focus on nonneoplastic monocytoses


Environmental Exposure

  • Alcoholic liver disease

  • Therapy related

    • Colony stimulating factor (CSF) therapy

    • Glucocorticoid administration

    • Drug-induced neutropenia or hemolytic anemia

    • Exogenous cytokine therapy

    • Postsplenectomy

  • Injury: Thermal injury, marathon running

Infectious Agents

  • Bacteria

    • Tuberculosis, brucellosis, subacute bacterial endocarditis, syphilis, Rocky mountain spotted fever

  • Virus

    • Cytomegalovirus, Epstein-Barr virus, varicella-zoster virus, parvovirus B19

  • Parasite

    • Malaria, visceral leishmaniasis

Inflammatory/Immune-mediated Disorders

  • Collagen vascular diseases

    • Systemic lupus erythematosus, rheumatoid arthritis, polyarteritis nodosa, temporal arteritis, myositis

  • Gastrointestinal disorders

    • Regional enteritis, ulcerative colitis, sprue

  • Liver diseases with increased bone marrow monocytes

    • Autoimmune hepatitis, primary biliary cirrhosis, non-immune-mediated cirrhosis

  • Sarcoidosis

  • Cytopenias

    • Immune-mediated hemolytic anemia

    • Immune-mediated thrombocytopenia


  • Hematopoietic disorders

    • Lymphoma (Hodgkin and non-Hodgkin), plasma cell myeloma, myelodysplastic syndrome

  • Nonhematopoietic tumors

    • Carcinomas and sarcomas

      • Common finding at diagnosis

    • Prominent monocytosis if M-CSF secreting tumor


  • Cytopenias

    • Hemolytic anemia

    • Chronic or congenital neutropenias

      • Wiskott-Aldrich syndrome

  • Myocardial infarction

Jun 13, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Monocytosis
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