From the Guidelines
Monocytosis is a significant indicator of an underlying condition, such as inflammation, infection, or malignancy, and its presence should prompt further investigation to identify the cause. The diagnosis of monocytosis is based on a monocyte count of more than 1x10^9/L, and it is essential to exclude reactive causes of monocytosis, such as infectious diseases and solid tumors, through a comprehensive diagnostic workup, including patient history, physical examination, complete blood count, and peripheral blood smear examination 1. The presence of monocytosis can be associated with various conditions, including chronic infections, inflammatory disorders, and certain cancers, such as leukemia and lymphoma. Key diagnostic criteria for chronic myelomonocytic leukemia (CMML), a type of cancer that can cause monocytosis, include persistent peripheral blood monocytosis, no Philadelphia chromosome or BCR-ABL1 fusion gene, and less than 20% blasts in the peripheral blood and bone marrow 1. The diagnostic workup for suspected CMML should include a bone marrow aspiration and biopsy, conventional cytogenetic analysis, and molecular assays to exclude certain genetic abnormalities 1. Treatment of monocytosis focuses on addressing the underlying condition, and monitoring monocyte levels can help track disease progression and treatment effectiveness. In clinical practice, the presence of monocytosis should be evaluated in the context of the patient's overall clinical presentation, and further investigation should be guided by the suspected underlying cause, as recommended by the Italian Society of Hematology and affiliated Societies 1. Some key points to consider when evaluating monocytosis include:
- Excluding reactive causes of monocytosis
- Conducting a comprehensive diagnostic workup, including bone marrow aspiration and biopsy
- Evaluating for underlying conditions, such as inflammation, infection, or malignancy
- Monitoring monocyte levels to track disease progression and treatment effectiveness.
From the Research
Significance of Monocytosis
- Monocytosis is a common finding caused by a wide variety of neoplastic and non-neoplastic conditions 2
- It is a frequently encountered clinical condition that needs appropriate investigation due to a broad range of differential diagnoses 3
- Monocytosis is a distinct but non-specific manifestation of various physiologic and pathologic conditions, including hematopoietic stem cell neoplasms 4
Diagnostic Approach
- The adequate evaluation of monocytosis involves the integration of laboratory data, morphology, clinical findings, and the judicious use of ancillary studies 2
- A stepwise diagnostic approach is recommended, including basic studies, flow cytometry, and molecular investigations to distinguish between different etiologies 3, 5
- The diagnosis of neoplastic monocytosis, such as chronic myelomonocytic leukemia, requires a laboratory-based approach and consideration of the genomic landscape of myeloid neoplasms 4
Clinical Implications
- Monocytosis is associated with an increased risk of haematological malignancy, particularly chronic myelomonocytic leukemia 6
- Sustained monocytosis further increases the risk of chronic myelomonocytic leukemia, although the diagnosis is still rare 6
- The absolute risk of haematological malignancy associated with monocytosis is low, and haematological malignancy should mainly be suspected when monocytosis is sustained or the clinical presentation raises suspicion of malignancy 6