White Blood Cell Counting in Severely Leukopenic Samples on a Sysmex XN Hematology Analyzer: Analytical Performance Evaluation of Whole Blood Mode and Low White Blood Cell Mode.

Abstract

Background: Sysmex XN-9100 (XN) measures WBC counts in whole blood (WB) mode and automatically switches to low WBC (LW) mode for leukopenic samples (WBC <0.50×10⁹/L). However, the analytical performance of LW mode in such samples has not been evaluated according to standard guidelines. We evaluated the analytical performance of the two modes in samples with WBC <0.50×10⁹/L.

Methods: Precision of WBC quantification in the two modes was evaluated using four samples according to the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) criterion (CV% 5.6). Linearity was evaluated at five concentrations. The two modes were compared in 650 leukopenic samples. Two samples showing discrepancies between the two modes were reviewed.

Results: WBC counting precision met the EFLM criterion for both modes, except in a sample with WBC <0.2×10⁹/L. Linearity was acceptable and within the allowable deviation of ±4.8% for both modes. Very high correlation (r=0.99), minimal mean difference (0.00×10⁹/L), and almost perfect agreement (κ=0.90) were noted. Discrepant samples were interpreted as clinically consistent in WB and LW modes in one case each.

Conclusions: This is the first study to evaluate the analytical performance of WBC counting in WB and LW modes on XN in samples with WBC <0.50×10⁹/L according to guidelines. The two modes demonstrated reliable analytical performance. As precision decreased at WBC <0.2×10⁹/L and discrepancies between the two modes were rare, careful attention is recommended.