Commutability of certified reference material ERM-DA 471/IFCC for cystatin C measurement

Objective To evaluate the commutability of certified reference material IRMM ERM-DA 471/IFCC for cystatin C measurement among 8 methods. Methods 46 individual samples used for the commutability study were residual serum samples collected from clinical laboratories. The individual samples interspersedwith pooled sera and the certified reference material IRMM ERM-DA 471/IFCC and the whole set of samples was divided into 2 subsets for measurements in 2 days. The measurements were performed by8 different methods o. The samples were measured in duplicate order. Calibration was performed every day. Passing-Bablok regression was performed to compare the slopes and intercepts of mean values of the serum samples derived from different methods. Pearson correlation cofficient was also calculated. Deming regeression and 95% confidence intervals were calculated to evaluate the statistics commutability of ERM-DA 471/IFCC. The minimal specification of bias derived from biological variations was calculated to evaluate the clinical commutability. Results The within-laboratory CVs of pool sera ranged from 0.5% to 4.0%. The Passing-Bablok slope ranged from 0.765 to 1.311 and intercepts ranged from -0.04 to 0.241. The determination coefficient of Pearson regression ranged from 0.988 to 0.999. Deming regeression and 95% confidence intervals demonstrated commutability of ERM-DA 471/IFCC in 4/28 (14.3%) methods pairs. The minimal specfication bias (5.12%)demonstrated commutability of ERM-DA 471/IFCC in15/28 (53.6%) methods pairs. Conclusions The ERM-DA 471/IFCC domonstrated poor commutability between some methods pairs. The commutability of ERM-DA 471/IFCC should be evaluated before used as calibrators. (Chin J Lab Med, 2015, 38: 306-309) Key words: Cystatin C; Reference standards; Laboratory proficiency testing