Decrease in the internal quality control intermediate reproducibility imprecision of Cystatin C results in China in the years from 2014 to 2023.

ObjectivesWe evaluated the intermediate reproducibility imprecision of cystatin C results based on internal quality control (IQC) data.MethodsIQC data for cystatin C analyte were collected each year from 2014 to 2023. We used the coefficient of variation (CV) to evaluate the level of laboratory imprecision. Five performance specifications [1/3 total allowable error (TEa), 1/4TEa and three levels performance specifications based on biological variation] were used to calculate the proportion of laboratories with CVs less than or equal to the performance specifications, namely, the pass rate. Based on the reference interval of Chinese adult serum cystatin C (0.59-1.03 mg/L), the concentration of quality control materials was divided into two levels for CV analysis: Level 1 (≤1.03 mg/L) and Level 2 (>1.03 mg/L). Additionally, group analysis was conducted according to the reagent manufacturer. Peer groups were further divided based on instruments to study differences between instruments. Boxplots were drawn to analyze trends in CVs, and differences in CVs among different groups were assessed using the Kruskal-Wallis test and Mann-Whitney U test.ResultsThe number of participating laboratories increased significantly from 255 in 2014 to 1814 in 2023. The intermediate reproducibility imprecision of Cystatin C IQC results in China had decreased from 5.1% (CV%) in 2014 to 3.3% in 2023. The pass rates based on 1/3 TEa showed upward trends increasing from 67% in 2014 to 88% in 2023. The pass rates for the other four performance specifications were all below 80%. The CVs of two concentration levels showed significant differences in most years. Roche Diagnostics reagent manufacturer exhibited low intermediate reproducibility imprecision. The BSBE-Abbott Architect series platform achieved a 100% pass rate based on 1/3 TEa in 2023.ConclusionsThe intermediate reproducibility imprecision of cystatin C has been a continuous overall improvement in China. However, the performance specifications of Cystatin C based on BV are currently not applicable to some laboratories in China. In addition, attention should be paid to the differences in intermediate reproducibility imprecision between various analysis systems.