title: 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Clinical Biochemistry Department, KAT General Hospital, Kifissia, Athens, Greece. Electronic address: kostas.makris.km@gmail.com.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Makris
authors.affiliation: Clinical Biochemistry Department, KAT General Hospital, Kifissia, Athens, Greece.
authors.forename: Efthimia
authors.initials: E
authors.lastname: Nikolaki
authors.affiliation: Clinical Biochemistry Department, KAT General Hospital, Kifissia, Athens, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Nanopoulos
authors.affiliation: Vascular Surgery Department, KAT General Hospital, Kifissia, Athens, Greece.
authors.forename: Konstantinos M
authors.initials: KM
authors.lastname: Pirgakis
authors.affiliation: Vascular Surgery Department, KAT General Hospital, Kifissia, Athens, Greece.
authors.forename: Chrisostomos K
authors.initials: CK
authors.lastname: Maltezos
mesh_terms: D001331:Automation; D001671:Biochemistry / Q000295:instrumentation*; D016022:Case-Control Studies; D055316:Cystatin C / Q000652:urine*; D006801:Humans; D007118:Immunoassay / Q000295:instrumentation* / Q000379:methods*; D007674:Kidney Diseases / Q000652:urine; D009391:Nephelometry and Turbidimetry / Q000295:instrumentation* / Q000379:methods*
chemical_list: D055316:Cystatin C
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