An elevated level of monocytes, which are a type of white blood cell, typically points to a chronic inflammation. Because monocytes live longer than neutrophils, which are the first type of white blood cell to respond to an infection, an elevated number of monocytes can be an indication of a long-lasting, or chronic, infection. An elevated level of monocytes is called monocytosis, and may also be indicative of other diseases or processes, such as immune-mediated disease, viral fever, Cushing's syndrome, stress response or sarcoidosis.
The role played by monocytes and their equivalent tissue-resident cell type, the macrophages, is to defend the body from intrusion by microorganisms by engulfing and digesting foreign particles. Monocytes are the largest of the leukocytes and account for between 2 to 10 percent of the white blood cell population in the human body. They can be found in all of the vertebrate species and are capable of arriving at the site of an infection within 8 to 12 hours. Monocytes also help to remove dead cells and other debris from the body. The process by which monocytes engulf, digest and destroy intruding microorganisms and unwanted substances is called phagocytosis.
A complete blood count, or CBC, with differential, is a commonly prescribed diagnostic blood test that provides a great deal of information regarding the condition of a patient's blood, and it can also bring to light possible disease indicators. A monocyte blood count is part of a CBC with differential, and the test also provides an overall white blood cell count, or WBC.