• Leukocytes, Monocytes
• Monocytes

• Lavender top tube
• 5 mL of whole blood

The WBC count and differential are a routine part of the complete blood count (CBC) test.

Monocytes are agranulocytes that seek antigens in the blood stream and eventually migrate to the tissues to become macrophages. Monocytes serve as an antigen-presenting cell for T lymphocytes.

• Leukocytes or WBCs are differentiated into 5 different types:
1. Basophils
2. Eosinophils
3. Lymphocytes
4. Monocytes
5. Neutrophils

The monocyte count is primarily useful in assessing patients with hematologic, neoplastic and inflammatory conditions; occasionally it may relate to an infectious process (viral, fungal, protozoal infections).

The White Blood Cell (WBC) count and differential, which the monocyte count is part of, has clinical utility in:

• Evaluation of infection or inflammation
• Assist in determination of viral versus bacterial infection
• Assist in evaluation of the stage and severity of an infection
• Detect allergic response or parasitic infections (elevated eosinophils)
• Evaluation for hematologic malignancy/disorders
• Detecting and identifying various types of myelopoietic disorders
• Detecting and identifying various types of leukemia
• Evaluating bone marrow depression
• Evaluation of need for further tests, such as manual WBC differential or bone marrow biopsy
• Evaluation of drug effects, response to chemotherapy or radiation
• Evaluation of effect of cytotoxic agents
• Screening test as part of a CBC on admission to a health care facility or before surgery

Additional information:

• The interpretation of a normal, high or low result of any given WBC type requires the context of the patient's clinical condition, history and physical examination
• Specific patterns of leukocyte response are seen in various types of diseases as determined by the differential count
• The life span of leukocytes is normally 13–20 days, after which the cells are destroyed in the lymphatic system and are excreted from the body in fecal matter.

Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.

WBC Differential

Monocytosis is the condition of increased monocytes. It is important that not only the differential shows increased monocytes, but that the absolute number of monocytes is increased also (>1,000 cells/mm³).

Conditions, which may cause monocytosis, include:

• Hematologic/Inflammatory disorders
• Collagen-vascular disease
• Polyarteritis nodosa (Periarteritis nodosa)
• Rheumatoid arthritis
• Systemic Lupus Erythematosus
• Hemolytic anemia
• Histiocytic medullary reticulosis
• Leukemia
• Acute monocytic
• Chronic myelogenous
• Chronic myelomonocytic
• Lymphomas
• Hodgkin's disease
• Non-hodgkin lymphomas
• Myeloproliferative disorders
• Agnogenic myeloid aplasia
• Myelosclerosis
• Polycythemia Vera
• Preleukemic states
• Infections
• Bacterial infections
• Brucellosis
• Listeria
• Subacute bacterial endocarditis
• Syphilis
• Tuberculosis
• Parasitic diseases
• Kala azar (Visceral Leishmaniasis)
• Malaria
• Viral infections
• Hepatitis
• Mumps
• Other infections
• Mycotic infections
• Protozoal infections
• Rickettsial infections
• Others
• Cirrhosis
• Histiocytosis
• Malignancies
• Regional ileitis
• Ulcerative colitis

Drugs causing monocytosis include:

• Alprazolam
• Ampicillin
• Carbenicillin
• Chlorpromazine
• Granulocyte colony-stimulating factor
• Griseofulvin
• Haloperidol
• Lomefloxacin
• Methsuximide
• Paroxetine
• Penicillamine
• Piperacillin
• Prednisone
• Propylthiouracil
• Quazepam

Monocytopenia is the condition of decreased monocytes. This is typically not of clinical significance.

Drugs causing decrease in monocytes include:

• Alprazolam
• Glucocorticoids (transient)
• Granulocyte colony-stimulating factor
• Triazolam

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• Amar D et al. Leukocytosis and increased risk of atrial fibrillation after general thoracic surgery. Ann Thorac Surg. 2006 Sep;82(3):1057-61; discussion 1061-2.
• Behrman: Nelson Textbook of Pediatrics, 17th ed. Chapter 710.
• Falcone FH et al. The 21^st century renaissance of the basophil? Current insights into its role in allergic responses and innate immunity. Exp Dermatol. 2006 Nov;15(11):855-64.
• LabTestsOnline®. White Blood Cell Count. [Homepage on the Internet] © 2001-2006. Last reviewed on May 6, 2005. Last accessed onOctober 17, 2006. Available at URL: http://www.labtestsonline.org/understanding/analytes/wbc/#how
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• Sanchez-Ramon S et al. Low blood CD8+ T-lymphocytes and high circulating monocytes are predictors of HIV-1-associated progressive encephalopathy in children. Pediatrics. 2003 Feb;111(2):E168-75.
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• http://www.med-ed.virginia.edu/courses/path/innes/wcd/leukocytosis.cfm
• http://www.med-ed.virginia.edu/courses/path/innes/wcd/leukopenia.cfm