Measurement of cystatin-C and creatinine in urine.
ABSTRACT The concentration of serum cystatin-C (Cys-C) is highly correlated with creatinine (Cr), and is mainly determined by glomerular filtration; thus, Cys-C may be an index of the glomerular filtration rate (GFR). However, the kinetics of urinary Cys-C and Cr excretions are unclear. Thus, we investigated the kinetics of urinary Cys-C and Cr excretions, and examined whether the urinary Cys-C concentration can be used as a marker of renal function.
The urinary excretion of Cys-C and Cr was evaluated in 1670 healthy subjects and 217 patients with proteinuria. We also investigated the urinary Cys-C concentration in 52 patients with chronic renal failure.
There was a good correlation between the urinary concentrations of Cys-C and Cr in the healthy group. This relation was also observed in patients showing persistent proteinuria without tubular cell damage. The mean urinary Cr concentration increased with age, and it was affected by the muscle mass. In contrast, the urinary Cys-C concentration was not affected by the muscle mass, and the concentration remained constant for all ages. We further found that the ratio of Cys-C to Cr (CCR) is a good index of the state of Cys-C reabsorption in the proximal tubules.
The urinary CCR can be a marker of renal tubular dysfunction. In addition, when CCR was in the normal range, the urinary Cys-C concentration accurately reflected the glomerular filtration function.
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ABSTRACT: Background: Formal validation of methods for biospecimen processing in the context of accreditation in laboratories and biobanks is lacking. A protocol for processing of a biospecimen (urine) was validated for fitness-for-purpose in terms of key downstream endpoints. Methods: Urine processing was optimized for centrifugation conditions on the basis of microparticle counts at room temperature (RT) and at 4°C. The optimal protocol was validated for performance (microparticle counts), and for reproducibility and robustness for centrifugation temperature (4°C vs. RT) and brake speed (soft, medium, hard). Acceptance criteria were based on microparticle counts, cystatin C and creatinine concentrations, and the metabolomic profile. Results: The optimal protocol was a 20-min, 12,000 g centrifugation at 4°C, and was validated for urine collection in terms of microparticle counts. All reproducibility acceptance criteria were met. The protocol was robust for centrifugation at 4°C versus RT for all parameters. The protocol was considered robust overall in terms of brake speeds, although a hard brake gave significantly fewer microparticles than a soft brake. Conclusions: We validated a urine processing method suitable for downstream proteomic and metabolomic applications. Temperature and brake speed can influence analytic results, with 4°C and high brake speed considered optimal. Laboratories and biobanks should ensure these conditions are systematically recorded in the scope of accreditation.Biopreservation and Biobanking 10/2014; 12(5). DOI:10.1089/bio.2014.0013 · 1.50 Impact Factor
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ABSTRACT: 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. ResultsThe 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 R2 = 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.Journal of Clinical Laboratory Analysis 09/2012; 26(5). DOI:10.1002/jcla.21531 · 1.14 Impact Factor
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ABSTRACT: Abstract Background: Pediatric studies are relatively scarce on the superiority of cystatin C over creatinine in estimation of glomerular filtration rate (GFR). This study measured cystatin C and serum creatinine levels, and compared GFR estimated from these two parameters in patients with chronic renal disease. Methods: This prospective, observational, controlled study included 166 patients aged 1-18 years diagnosed with stage I to III chronic renal disease, and 29 age- and sex-matched control subjects. In all patients, GFR was estimated via creatinine clearance, Schwartz formula, Zappitelli 1 and Zappitelli 2 formula and the results were compared using Bland-Altman analysis. Results: Patients and controls did not differ with regard to height, body weight, BMI, serum creatinine and serum cystatin levels, and Schwartz formula-based GFR (p > 0.05). There was a significant relationship between creatinine and cystatin C levels. However, although creatinine levels showed a significant association with age, height, and BMI, cystatin C levels showed no such association. ROC analysis showed that cystatin C performed better than creatinine in detecting low GFR. Conclusion: Cystatin C is a more sensitive and feasible indicator than creatinine for the diagnosis of stage I to III chronic renal disease.Renal Failure 02/2015; DOI:10.3109/0886022X.2015.1014771 · 0.94 Impact Factor