From the Guidelines
Monocytosis is primarily caused by infections, inflammatory conditions, and certain malignancies, with bacterial infections like tuberculosis, endocarditis, and typhoid fever being common triggers, as well as fungal and protozoal infections, according to 1 and 1.
Causes of Monocytosis
The causes of monocytosis can be broadly categorized into:
- Infections: Bacterial infections such as tuberculosis, endocarditis, and typhoid fever, as well as fungal and protozoal infections, can trigger elevated monocyte counts, as noted in 1.
- Inflammatory conditions: Chronic inflammatory disorders like inflammatory bowel disease, rheumatoid arthritis, and sarcoidosis frequently lead to monocytosis, as mentioned in 1.
- Malignancies: Hematologic malignancies, particularly chronic myelomonocytic leukemia, acute monocytic leukemia, and Hodgkin lymphoma, are significant causes of monocytosis, as discussed in 1.
Physiological Response
Monocytes increase during these conditions because they are critical components of the innate immune system that respond to infection and inflammation by differentiating into macrophages and dendritic cells at sites of injury, participating in phagocytosis, antigen presentation, and cytokine production, as implied by the diagnostic workup for suspected CMML in 1.
Diagnostic Considerations
A diagnostic workup for suspected CMML should include a patient's history, physical examination, complete blood count, peripheral blood smear examination, bone marrow aspiration, and biopsy, as well as molecular assays to exclude certain genetic abnormalities, as recommended in 1. The most recent and highest quality study, 1, provides a comprehensive approach to diagnosing the causes of monocytosis, emphasizing the importance of a thorough diagnostic workup to exclude reactive causes of monocytosis and to identify underlying conditions that may be contributing to the elevated monocyte count.
From the Research
Causes of Monocytosis
- Monocytosis is caused by a wide variety of neoplastic and non-neoplastic conditions 2
- The condition can be due to different etiologies, including chronic myelomonocytic leukemia, a prototypical neoplasm with monocytosis, as well as other reactive or neoplastic causes 3
Diagnostic Approach
- A stepwise diagnostic approach is necessary for a patient presenting with monocytosis, involving the integration of laboratory data, morphology, clinical findings, and ancillary studies 2, 3
- Flow cytometry studies can help distinguish between different causes of monocytosis, such as chronic myelomonocytic leukemia and other reactive or neoplastic causes 3