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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 (LoQ), recovery, assay precision, stability, and interference caused by hemoglobin were evaluated. RESULTS: The LoQ 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 +4C. 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. |
