Referral Guidelines for Monocytosis

Introduction to Monocytosis

• Patients with persistent monocytosis (>1×10^9/L) should be referred to a hematologist for evaluation, particularly when the monocytosis is sustained for at least 3 months without evidence of other causes such as infection, inflammation, or malignancy 1
• Monocytosis can be either reactive or neoplastic, with reactive monocytosis commonly seen in infections and inflammatory conditions 2

Diagnostic Criteria

• The presence of dysplastic features in blood cells, abnormal peripheral blood smear showing immature myeloid cells, and splenomegaly or hepatomegaly are indicators for urgent referral to a hematologist 1, 4
• Persistent monocytosis (>1×10^9/L) with concurrent unexplained cytopenias is an indication for urgent referral 2, 3

Referral Algorithm

• The American College of Hematology recommends referral to a hematologist for patients with persistent monocytosis (>1×10^9/L) for ≥3 months without clear reactive cause 1
• Patients with monocytosis and abnormal blood counts in other cell lines should be referred to a hematologist for evaluation 3
• Monocytosis with unexplained symptoms such as fatigue, weight loss, and night sweats is an indication for referral to a hematologist 1

Diagnostic Workup

• A complete blood count with differential, peripheral blood smear examination, basic metabolic panel, and liver function tests should be considered before referral to a hematologist 1, 2, 3
• Inflammatory markers such as ESR and CRP should be evaluated in patients with monocytosis 2

Key Distinguishing Features of CMML

• The European Hematology Association recommends that CMML be diagnosed based on persistent peripheral blood monocytosis (>1×10^9/L), monocytes accounting for ≥10% of white blood cells, and dysplastic features in one or more cell lines 1
• The absence of Philadelphia chromosome or BCR-ABL1 fusion gene, and no rearrangement of PDGFRA or PDGFRB are also key distinguishing features of CMML 1

Clinical Considerations

• The International Society for Immunotherapy of Cancer recommends that patients receiving immune checkpoint inhibitors be monitored for post-treatment lymphocytosis, eosinophilia, neutrophilia, and monocytosis, which are not typically clinically significant 2, 3
• Patients with unexplained cytopenias should be referred to hematology for evaluation, as recommended by the American Society of Hematology 3