Impact of Type A Standard Measurement Uncertainty in the Primary Reference Measurement Procedure for Creatinine Assay on Bias Analysis in Accuracy-Based Creatinine Proficiency Testing

Background:The accuracy-based creatinine (ABCr) proficiency testing (PT) program by the Korean Association of External Quality Assessment Service evaluates bias and acceptability in participating laboratories using target values assigned by the primary reference measurement procedure (RMP).This study evaluated the impact of type A standard measurement uncertainty (MU) in the primary RMP on bias and acceptability assessments.Methods: ABCr PT data from 2020 to 2021 were analyzed.Using the target mean, standard deviation, and number of replicates provided by the Reference Material Institute for Clinical Chemistry Standards laboratory (Japan), the type A MU for each sample was calculated using a bottom-up approach.Bias and acceptability of creatinine assays were compared with and without the inclusion of type A MU when assigning target values. Results:The type A MU of the primary RMP for the creatinine assays ranged from 0.01 to 0.02 mg/dL depending on the sample.Without type A MU, the mean bias of creatinine assay ranged from -2.9% to 6.5%.Incorporating type A MU into target values, adjusted the mean bias to -3.2% to 5.3% (with addition) and -2.6% to 7.8% (with subtraction).Acceptability rates ranged from 69.2% to 95.0% without type A MU and shifted to 70.1% to 95.1% (with addition) and 68.5% to 95.4% (with subtraction).Conclusions: The inclusion of type A MU in the primary RMP affects bias and acceptability assessment, highlighting its significance in the interpretation of ABCr PT results.