From the Guidelines
Monocytosis is a condition that requires thorough evaluation to determine its underlying cause, and management should focus on treating the underlying condition rather than the monocytosis itself. This condition is characterized by an elevated number of monocytes in the blood, typically above 1x10^9/L 1. The diagnostic criteria for 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.
Causes of Monocytosis
The causes of monocytosis can be varied and include:
- Chronic infections such as tuberculosis or endocarditis
- Inflammatory disorders like inflammatory bowel disease or rheumatoid arthritis
- Certain cancers, particularly leukemias and lymphomas
- Recovery from bone marrow suppression
Management of Monocytosis
Management of monocytosis focuses on treating the underlying cause rather than the monocytosis directly 1. No specific medication targets monocytosis alone. If you have monocytosis, your healthcare provider will likely conduct additional tests to determine the cause, which may include blood cultures, imaging studies, or bone marrow examination in some cases 1.
Importance of Monocytes
Monocytes are important immune cells that develop into macrophages in tissues and play crucial roles in fighting infections and removing dead cells 1. Their elevation signals that your immune system is responding to something, which is why identifying the underlying trigger is essential for proper treatment. In some cases, monocytosis may be associated with intracellular pathogens such as Salmonella 1.
Diagnostic Approach
The diagnostic approach to monocytosis may involve a range of tests, including:
- Blood cultures
- Imaging studies
- Bone marrow examination
- Endoscopy with small bowel biopsy for diagnosis of certain infections
- Sigmoidoscopy with biopsy of abnormal mucosa to differentiate infectious colitis from inflammatory bowel disease 1.
In summary, monocytosis requires a thorough diagnostic evaluation to determine its underlying cause, and management should focus on treating the underlying condition.
From the Research
Definition and Diagnosis of Monocytosis
- Monocytosis is a frequently encountered clinical condition that requires appropriate investigation due to a broad range of differential diagnoses 2.
- The adequate evaluation of monocytosis involves the integration of laboratory data, morphology, clinical findings, and the judicious use of ancillary studies 3.
- Monocytosis is a distinct but non-specific manifestation of various physiologic and pathologic conditions, including neoplastic and non-neoplastic conditions 4.
Causes and Associations of Monocytosis
- Monocytosis may be a consistent and integral component of diseases such as chronic myelomonocytic leukemia (CMML) or acute myeloid leukemia with monocytic differentiation 4.
- Monocytosis can also be associated with other haematological malignancies, including myeloproliferative neoplasms (MPN) and myelodysplastic syndromes (MDS) 5.
- In primary care, monocytosis is a relatively common finding, but its predictive value for haematological malignancy is unknown, although it is associated with an increased risk of all types of haematological malignancy 6.
Diagnostic Approach to Monocytosis
- A stepwise diagnostic approach is recommended for patients presenting with monocytosis, including basic studies, flow cytometry, and molecular investigations 2, 4.
- The differential diagnosis between CMML, MPN, and MDS with monocytosis can be challenging and may require histological, immunohistochemical, and phenotypic flow cytometric studies 5.
- Sustained monocytosis (at least two requisitions in 3 months) can further increase the risk of CMML, although the diagnosis is still rare 6.