Utility of Reference Change Values for Delta Check Limits

Objectives To assess the utility of reference change values (RCVs) as delta check limits. Methods A total of 1,650,518 paired results for 23 general chemistry test results from June 1, 2014, to October 31, 2016, were analyzed. The RCVs for each analyte were calculated from the analytical imprecision and within-subject biological variation. The percent differences between two consecutive results in one patient were categorized into one of four groups: outpatients, inpatients, emergency care, and general health care. For each, 2.5th and 97.5th percentile values were computed and compared with their RCVs. The distributions were assessed for normality using the Kolmogorov-Smirnov test. Results Most of the estimated limits were larger than the corresponding RCVs and, furthermore, with notable differences across the groups. Patients in the emergency care group usually demonstrated larger delta percent values than those in the other groups. None of the distributions of the percent differences passed tests of normality when subjected to Kolmogorov-Smirnov analysis. Conclusions Comparison of estimated RCVs and real-world patient data revealed the pitfalls of applying RCVs in clinical laboratories. Laboratory managers should be aware of the limitations of RCVs and exercise caution when using them.