Optimization of Leukocytic Flags in the Sysmex‐ XN Series With the Help of Flow Cytometric Differential ( FlowDiff ) Can Significantly Optimize Laboratory Efficiency

ABSTRACT Objectives The aim of this study was to adjust the default white blood cell (WBC) differential count flag settings on the Sysmex XN‐9100 haematology analyser to reduce unnecessary additional leukocyte differential counts without compromising diagnostic sensitivity. Methods Data from 4554 routine blood samples flagged on Sysmex XN‐9100 and corresponding additional leukocyte differential counts performed on the Sysmex XF‐1600 flow cytometer were used to optimise the WBC flagging rules. Results A total of 1148 samples had scattergram‐related flags, which are non‐adjustable. Optimal cut points for Q‐flags were established based on Youden's Index for the remaining 3406 samples, while the diagnostic sensitivity of the new flagging rules for acute leukaemia was assessed in a validation cohort. The optimal cut points for Q‐flags were 120 for ‘Atypical Lymphocytes’, 170 for ‘Abnormal Lymphocytes’ and 160 for ‘Blasts’, while the Q‐flag ‘Left shift’ offered no diagnostic value in our cohort. The count flags ‘eosinophilia’, ‘basophilia’ and ‘monocytopenia’ were deactivated, as the results from Sysmex XN were comparable to the flow cytometric reference method. By implementing the new flagging rules, 1709 (37.5%) of the samples would have been processed without need for additional leukocyte differential count. When evaluated in a separate validation cohort of 90 samples from patients with newly diagnosed acute leukaemia, the new rules showed similar diagnostic sensitivity to the default flagging system. Conclusion Optimisation of Sysmex flagging rules for leukocyte differential counts was feasible and significantly reduced unnecessary reflex testing, while maintaining analytical accuracy and diagnostic safety.