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Introduction: Immature granulocyte percentage (IG%) is an important biomarker for infection control. We observed spurious cases where the IG% was dramatically underestimated on the automated Sysmex XN‐series hehmatology analyzer compared with manual differential. These cases were associated with high values of "Neutrophil Reactivity Intensity" (NEUT‐RI), which should reflect the metabolic activity of the neutrophils. Methods: We conducted a three‐stage study to evaluate whether NEUT‐RI could be utilized to screen for misclassified IG% results defined as the manual differential estimating a 10 percentage points higher IG% compared with the automated Sysmex differential. First, 124 patient samples were selected for 800‐cell manual smear analysis based on their NEUT‐RI values and compared with the automatic Sysmex IG% results. Next, 11 098 routine 110‐cell manual smear analyses were compared with the corresponding Sysmex IG% results. Finally, during a 19‐day period 160 additional patient samples underwent smear based on NEUT‐RI values ≥56 fluorescence intensity (FI) to screen for misclassified results beyond our current smear practice. Results: NEUT‐RI ≥56 predicted IG% misclassification with 91% sensitivity and 88% specificity, but primarily when the internal Sysmex flag "Abnormal WBC Scattergram" was present. 90.1% of misclassified results were identified by this flag. Beyond our existing smear rules including this flag, NEUT‐RI ≥56 FI had a positive predictive value below 1%. Conclusion: Both NEUT‐RI and the internal Sysmex flag "Abnormal WBC Scattergram" work well to identify cases of IG% misclassification. However, in our setting NEUT‐RI ≥56 FI had no meaningful additional predictive capacity to identify misclassifications beyond our current smear rules. [ABSTRACT FROM AUTHOR]