What are the implications of elevated monocyte (white blood cell) count?

From the Guidelines

Elevated monocytes, or monocytosis, is a condition that requires prompt medical evaluation to determine the underlying cause, which could be an infection, inflammation, or other health condition, and treatment should focus on addressing this underlying cause to improve morbidity, mortality, and quality of life. Monocytosis can be associated with various conditions, including bacterial infections like tuberculosis or endocarditis, certain viral infections, autoimmune disorders such as lupus or rheumatoid arthritis, some cancers, and chronic inflammatory conditions 1. The normal range for monocytes is typically 2-8% of the total white blood cell count, and values above this threshold warrant investigation but aren't always cause for serious concern.

Key Considerations

• Monocytes play a crucial role in the immune system by engulfing pathogens and cellular debris, and their elevation is the body's natural response to fighting infection or dealing with inflammation.
• A high total white blood cell count and neutrophil count often occur in patients with severe infections, and monocyte predominance may suggest the presence of an intracellular pathogen such as Salmonella 1.
• In patients with COVID-19, monocyte and macrophage hyperactivation may contribute to increased circulating levels of pro-inflammatory cytokines, which can lead to cardiovascular risk and other complications 1.
• Treatment for monocytosis depends on the underlying cause and may involve antibiotics for bacterial infections, antiviral medications for viral infections, or other therapies for autoimmune disorders or cancers.

Recommendations

• If your blood test shows elevated monocytes, consult with your healthcare provider for proper evaluation and additional tests to determine the cause.
• Maintain good health practices, including adequate rest, hydration, and nutrition, while waiting for your appointment.
• The most critical step in managing elevated monocytes is to identify and treat the underlying cause, which can significantly impact morbidity, mortality, and quality of life.

From the Research

Causes of Elevated Monocytes

• Monocytosis is a common finding caused by a wide variety of neoplastic and non-neoplastic conditions 2
• Elevated monocytes can be seen in conditions such as chronic myelomonocytic leukemia, a prototypical neoplasm with monocytosis 3
• Monocytosis can also be caused by reactive conditions, such as inflammation or infection 4

Diagnosis of Elevated Monocytes

• The diagnosis of monocytosis involves the integration of laboratory data, morphology, clinical findings, and the judicious use of ancillary studies 2
• A complete blood count (CBC) is one of the most frequently ordered laboratory tests in medicine and can help in the diagnosis of monocytosis 5
• Flow cytometry studies can help distinguish between different etiologies of monocytosis, such as chronic myelomonocytic leukemia and reactive causes 3

Association with COVID-19

• Elevated circulating monocytes and monocyte activation have been observed in COVID-19 convalescent individuals 6
• Monocyte alteration and increased activated monocyte subsets may impact pulmonary function in COVID-19 convalescents 6

Diagnostic Approach

• A systematic approach to the diagnosis of monocytosis is necessary, including a stepwise diagnostic approach and the use of ancillary studies such as flow cytometry 3
• The differential diagnosis between different entities, such as CMML, MPN, and MDS with monocytosis, can be challenging and may require molecular investigations and elimination of any reactive cause of monocytosis 4