This week’s case featured a 61-year-old patient who presented with persistent fatigue and was found to have abnormal haematology results during routine testing. Further review in the haematology laboratory was requested.

The full blood count result showed:

• WBC: 50.4 × 10⁹/L (elevated)
• RBC: 2.96 × 10¹²/L (low)
• Haemoglobin: 84 g/L (anaemia)
• Haematocrit: 0.245
• MCV: 91.5 fL (normocytic)
• MCH: 28.4 pg
• MCHC: 339 g/L
• RDW: 15.2%
• Platelets: 122 × 10⁹/L (mild thrombocytopenia)

Given the analyser’s inability to differentiate the cells, a manual differential count was performed:

• Neutrophils: 16%
• Lymphocytes: 14%
• Monocytes: 70%

Blood film findings:

• Marked monocytosis
• Numerous mature monocytes
• Normocytic anaemia
• Mild thrombocytopenia

Flow cytometry confirmed a significant clonal monocytic population with an immunophenotype consistent with a monocytic lineage. Typical markers supportive of this pattern include:

• Myeloid/monocytic markers (e.g., CD33, CD13, CD64, CD14, CD11b)
• CD45 bright, CD117 partial, CD34 variable/negative

Together, these results supported a clonal monocytic expansion rather than reactive monocytosis.

The combined clinical, haematological, and immunophenotypic findings are consistent with Chronic Myelomonocytic Leukaemia (CMML). CMML is an overlap myelodysplastic/myeloproliferative neoplasm and requires integration of morphology and immunophenotyping.