Measurement of Urinary Cystatin C with a Particle‐Enhanced Turbidimetric Immunoassay on Architect C i8200

Background Cystatin C is a low‐molecular‐weight protein that is freely filtered by the glomerulus and catabolized after reabsorption by the proximal tubular cells in healthy subjects. Urinary cystatin C is a potential biomarker for tubular damage including acute kidney injury ( AKI ) in the acute phase when patients are submitted to the intensive care unit. Methods The aim of this study was to perform a method validation of urinary analysis of cystatin C by particle‐enhanced turbidimetric immunoassay ( PETIA ) on a high‐throughput chemical analyzer. Total assay time was 10 min. The antigen excess, linearity, lower limit of quantification ( L o Q ), recovery, assay precision, stability, and interference caused by hemoglobin were evaluated. Results The L o Q was calculated to 0.020 mg/l with a coefficient of variation ( CV ) ≤ 10%. No hook effect was observed and the assay was linear over the studied interval less than 0.020–0.950 mg/l with a regression of R 2 = 0.9994. The assay had a recovery between 93–100% and the assay precision had a total CV of less than 3.5%. Cystatin C was stable for 3 days in room temperature and 14 days in +4 C . The assay did not show any major interference with hemoglobin at a hemoglobin concentration of 10 g/L. The reference interval for urine cystatin C was less than 0.166 mg/l. Conclusion The urinary cystatin C PETIA showed good precision and performance characteristics including short test turnaround times that are necessary qualifications for a biomarker at a routine laboratory. J. Clin. Lab. Anal. 26:358‐364, 2012. © 2012 Wiley Periodicals, Inc.