To assess the consistency of four standardized cystatin C particle-enhanced turbidimetric assay (PETIA) and one particle-enhanced nephelometric immunoassay(PENIA) measurement systems

Performance verification test was conducted according to CLSI EP15-A2 and EP9-A2. Fourty serum samples in comparative test were obtained from the remaining serum samples of outpatients in Peking Union Medical College Hospital in March 2013. Fourty serum samples were tested on Olympus AU5400 automatic biochemical analyzer (four PETIA Cys C reagents: Shanghai Jingyuan Co., Ltd, Beijing Leadman Biochemistry Co., Ltd, Beijing Strong Biotechnologies, Maker Biotechnology in Sichuan, and labelled as A, B, C, D respectively) and PENIA N Latex Cys C measurement system on Siemens BNⅡ (labelled as E). Correlation analysis were performed among four PETIA methods one PENIA method Differences of each detection system were compared in the medical decision level 1,2,3,4 mg/L. The reference material ERM-DA471/IFCC was measured by five systems and bias (percentage bias) was calculate for each system.

Results of systems A, B, C, D, E were 1.29（0.89-2.43）, 1.30（0.96-2.59）, 1.22（0.90-2.44）, 1.27（0.96-2.47）, 1.14（0.82-2.05）mg/L. Chart shows bias among these five systems was small when Cys C concentration was less than 4mg/L. PETIA method A, B, C, D correlated with their mean value well, with the average deviation from their mean value (percent deviation) at -0.017-0.031 mg/L (-3.1%-2.1%), and all were less than allowed bias from the biological variation (3.4%). The deviation of PETIA method A, B, C, D with their mean value in medical decision level at -0.176-0.178 mg/L. Systems A, B, C, D correlated well with the result of PENIA method system E , and the mean deviation (percent deviation) was at 0.278-0.326 mg/L (12.6%-18.5%), and the deviation (percent deviation) in the medical decision level 0.055-1.079 mg/L (5.51%-26.98%). Bias of PETIA method A, B, C, D Cys C system measuringERM-DA471/IFCC ranged from 0.22 to 0.39 mg/L (3.9%-7.0%), which exceeded the allowable range of the reference material target value, and were larger than the allowable bias from biological variation (3.4%). Bias (percent) of PENIA method system E was -0.1 mg/L (-1.7%), within the allowable range of ERM-DA471/IFCC target value.

The consistency of four assesed PETIA Cys C reagents was relatively ideal, and improved markably after being traced to ERM-DA471/IFCC. Besides, the results of PETIA were higher than those of PENIA. Bias among these five systems was small when Cys C concentration was less than 4 mg/L, and the bias became larger in higher Cys C concentration.（Chin J Lab Med,2014,37:362-367）

Cystatin C; Nephelometry and turbidimetry; Immunoassay; Reproducibility of results; Reference standards