Monocytopenia in hairy cell leukemia, a difficult feature to detect using sysmex XN series hematology analyzer

Abstract

Hairy cell leukemia (HCL) is a relatively rare chronic B-cell malignancy that involves the bone marrow, spleen and peripheral blood. Monocytopenia could represent a clue for the suspicion of HCL with complete blood counts (CBCs) and careful assessment of the cell morphology being the first steps in the identification of hairy cells. The purpose of our study is to describe our experience with cell count and flag performance provided by the XN-module in a continuous series of six HCL patients diagnosed in the last two years. The final diagnosis was made by immunophenotypic and genetic analysis. Five out of six patients presented relative monocytosis on automated differential count. Nevertheless, the relative monocyte count was overestimated by the analyzer regarding to the manual count in all cases. The smear revision showed that most cells classified as monocytes were primarily hairy cells which afterwards were confirmed by the immunophenotype. All patients showed potentially pathologic WDF scatergrams or flags and were selected for microscopic smear review. In five of the six patients the WDF channel displayed the “Blasts/Abn Lympho?” flag and triggered the reflex reanalysis using the WPC channel. All samples presented lack or abnormal position of the monocytes cluster in the WPC scattergram. As a conclusion the monocytopenia should be taken with caution for the initial screening of hairy cell leukemia. Instead, an abnormal appearance of WDF scattergram and the lack or an ectopic position of the monocyte cluster in WPC scattergram should be considered to initiate the review of the peripheral blood smear.