Introduction: The Sysmex XN-1000 autoanalyzer is designed to improve the analytical performance for counting blood cell and abnormal cell flags specificity. Each laboratory has its own decision to change the trigger thresholds for many of these flags. This would safely decrease the number of unnecessary blood film reviews, reduce the workload, and improve the turnaround time. Objective: The aim of the current study was to assess the performance of the thresholds at which Sysmex XN-1000 white blood cell specific flags (“Blast/Abnormal lymphocytes", “Atypical lymphocytes" “Left Shift", and “Immature granulocytes") are triggered as well as to optimize those trigger thresholds in order to raise the positive predictive value (PPV) of our system of flags for those specific abnormalities. Materials and Methods: Microscopic slide review was done for 400 blood samples when one or more of the interest flags were triggered using the factory default settings. Results: For all flags (“Blast/Abnormal lymphocytes", “Atypical lymphocyes" “Left Shift", and “Immature granulocytes"), the sensitivity was excellent (100%, 92.8%, 91%, and 95.8%, respectively) but the specificity was much less (14.2%, 19.3%, 25% and 1.9%, respectively). A statistical method (Youden Index) was applied for optimizing the thresholds of the 4 flags aiming at improving their specificity. Statistically speaking, the optimal thresholds for best efficiency were 290 for the “Blast/Abnormal lymphocytes" flag, 150 for the “Atypical lymphocytes" flag, 190 for the “Left Shift" flag and 0.42×10³/µL for the “Immature granulocytes" flag. Conclusion: Considering the clinical impact of the abnormalities that are suspected when a flag is activated, it was prudent to privilege sensitivity over specificity and   keep both the “Blast/Abnormal lymphocytes" and the “Immature granulocytes" flagging thresholds at the factory default settings in order not to miss any cases of clinical importance. On the other hand, the thresholds of “Atypical lymphocytes" flag can probably be safely raised to 150 and the “Left Shift" flag to 190, thus reducing the number of unduly triggered samples while maintaining the sensitivity clinically acceptable.