Monocytosis / Monocytic Dysplasia: Testing a New Diagnostic Tool Using Sysmex XN Analyzer Parameters

Background: In a medical laboratory, monocytosis is very common, often reactive, but may be related to a hematological malignancy, particularly Chronic myelomonocytic leukemia (CMML).

CMML is considered a diagnosis of elimination given the frequency of reactive monocytosis. This increases the number of blood smears (BS) performed without diagnostic interest. The objective of this study is to test and validate on our population a score established from the parameters of SYSMEX XN analyzers, to differentiate patients with monocytic dysplasia - which may suggest a hematological malignancy, in particular CMML -, from patients with reactive monocytosis, and reduce the number of unnecessary BS.

Methods: Patients aged ≥18 years with monocytosis>1G/L and>10% leukocyte formula were included. BS were performed manually with the objective of confirming monocytosis and looking for signs of monocytic dysplasia. The calculation of the monodysplasia score (MS) was performed using parameters derived from the SYSMEX XN9100 analyzer.

Results: During the study period 263 patients were collected with a sex-ratio of 1.4. The mean monocyte value was 1.49 G/L. The MS was <0.160 in 242 patients, and >0.160 in 21 patients of which 12 showed signs of monocytic dysplasia on BS. The MS showed 100% sensitivity and 96.41% specificity with a negative predictive value at 100% and a positive predictive value at 57.14%.

Conclusion: Our study demonstrates the effectiveness of MS, having shown high sensitivity and specificity. The diagnosis of CMML remains difficult, so the use of MS helps to select patients most suspected of malignancy and will reduce the number of unnecessary BS.