A Method for Optimizing and Validating Institution-Specific Flagging Criteria for Automated Cell Counters

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Abstract
Context. —Automated cell counters use alerts (flags) to indicate which differential white blood cell counts can be released directly from the instrument and which samples require labor-intensive slide reviews. The thresholds at which many of these flags are triggered can be adjusted by individual laboratories. Many users, however, use factory-default settings or adjust the thresholds through a process of trial and error. Objective. —To develop a systematic method, combining statistical analysis and clinical judgment, to optimize the flagging thresholds on automated cell counters. Design. —Data from 502 samples flagged by Sysmex XE-2100/5000 (Sysmex, Kobe, Japan) instruments, with at least 1 of 5 user-adjustable, white blood cell count flags, were used to change the flagging thresholds for maximal diagnostic effectiveness by optimizing the Youden index for each flag (the optimization set). The optimized thresholds were then validated with a second set of 378 samples (the validation set). Results. —Use of the new thresholds reduced the review rate caused by the 5 flags from 6.5% to 2.9% and improved the positive predictive value of the flagging system for any abnormality from 27% to 37%. Conclusions. —This method can be used to optimize thresholds for flag alerts on automated cell counters of any type and to improve the overall positive predictive value of the flagging system at the expense of a reduction in the negative predictive value. A reduced manual review rate helps to focus resources on differential white blood cell counts that are of clinical significance and may improve turnaround time.

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