Measurement of cystatin C in human urine by particle-enhanced turbidimetric immunoassay on an automated biochemistry analyzer

Abstract

Background: Cystatin C (CysC), is produced by all the nucleated cells of the human body, is freely filtered by the kidney glomerulus and reabsorbed by the tubules. It is widely accepted that no tubular secretion of CysC occurs. Raised urinary levels are believed to indicate tubular damage.

Methods: We report here the validation of a quantitative assay to measure urinary cystatin C (uCysC) using a commercial CysC kit based on a latex particle-enhanced turbidimetric immunoassay (PETIA), on an automated biochemistry analyzer. The clinical relevance of this assay was tested on several kidney disease patients and a reference range was determined using healthy controls.

Results: The assay is precise (total CV<4%), and sensitive (limit of quantification=0.06 mg/dL, and limit of detection=0.02 mg/L). Calibration is stable for at least 30 days. The assay showed very good linearity over the studied interval (0.02 to 2.25mg/L). Recovery ranged from 101.62 to 106.49%. The analyte is stable, at 4°C for at least 2 days, and at 20°C for 48 h. The upper reference value was 0.12 mg/L Median uCysC concentration in 30 acute kidney injury patients (1.47 mg/L, interquartile range=0.27-3.87 mg/L) and was significantly higher than that in 25 patients with normal kidney function (0.05, 0.03-0.12; p<0.0001), 30 patients with chronic kidney disease (0.13, 0.05-0.77; p<0.0001) and 15 patients with pre-renal azotemia (0.15, 0.08-0.31; p<0.0001).

Conclusion: Our data indicate that uCysC can be processed on automated biochemistry analyzers and its measurement could easily be added to a standard panel to screen kidney diseases.

Keywords: (AKI); (CysC); (PETIA); (uCysC); Acute kidney injury; Cystatin C; Particle-enhanced turbidimetric immunoassay; Tubular damage; Urinary cystatin C; acute kidney injury; cystatin C; particle-enhanced turbidimetric immunoassay; urinary cystatin C.