title: Measurement of urinary cystatin C by particle-enhanced nephelometric immunoassay: precision, interferences, stability and reference range.
abstract: BACKGROUND
  Urinary excretion of the low molecular weight protein cystatin C is a marker of renal disorders and a good predictor of the severity of acute tubular necrosis. We evaluated the measurement of urinary cystatin C and determined its reference range.
  
  
  METHODS
  Measurement of urinary cystatin C by particle-enhanced nephelometric immunoassay (PENIA) in 102 patients with various renal disorders and 133 healthy controls. We assessed the influence of pH and temperature, interferences on urinary cystatin C measurement, as well as cystatin C adsorption to plastic.
  
  
  RESULTS
  The upper reference value for urinary cystatin C was 0.28 mg/L, independent of age and gender. Accuracy and linearity (r(2)=0.996) were excellent. Intra- and inter-assay precision were < or =4.8% and < or =5.2%, respectively. Albumin (< or =160 g/L), bilirubin (< or =500 micromol/L) and haemoglobin (< or =210 micromol/L) did not show interferences. Urinary cystatin C was stable, at urine pH> or =5, at -20 degrees C and 4 degrees C for 7 days, and at 20 degrees C for 48 h. Freezing and thawing did not influence urinary cystatin C concentration. There was no adsorption of cystatin C to plastic.
  
  
  CONCLUSIONS
  Urinary cystatin C measurement by PENIA is precise. High stability and no interference add to the practicability of urinary cystatin C as a routine biochemical test.
authors.affiliation: Department of Nephrology, University Hospital, D-45122 Essen, Germany. herget.rosenthal@t-online.de
authors.forename: Stefan
authors.initials: S
authors.lastname: Herget-Rosenthal
authors.forename: Thorsten
authors.initials: T
authors.lastname: Feldkamp
authors.forename: Lothar
authors.initials: L
authors.lastname: Volbracht
authors.forename: Andreas
authors.initials: A
authors.lastname: Kribben
mesh_terms: D000328:Adult; D000368:Aged; D002138:Calibration; D055316:Cystatin C; D015891:Cystatins / Q000652:urine*; D005260:Female; D006801:Humans; D007118:Immunoassay; D007674:Kidney Diseases / Q000652:urine*; D008297:Male; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry; D011237:Predictive Value of Tests; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins