title: Measurement of urinary cystatin C with a particle-enhanced turbidimetric immunoassay on Architect ci8200.
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.
  
  
  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 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Medical Sciences, Clinical Chemistry, Uppsala University, Uppsala, Sweden.
authors.forename: Feria Hikmet
authors.initials: FH
authors.lastname: Noraddin
authors.forename: Mats
authors.initials: M
authors.lastname: Flodin
authors.forename: Annika
authors.initials: A
authors.lastname: Fredricsson
authors.forename: Azita
authors.initials: A
authors.lastname: Sohrabian
authors.forename: Anders
authors.initials: A
authors.lastname: Larsson
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D030161:Avian Proteins; D015415:Biomarkers / Q000737:chemistry / Q000652:urine; D055316:Cystatin C / Q000737:chemistry / Q000652:urine*; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007136:Immunoglobulins; D008297:Male; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D055550:Protein Stability; D012044:Regression Analysis; D012680:Sensitivity and Specificity
chemical_list: D030161:Avian Proteins; D015415:Biomarkers; D055316:Cystatin C; C016512:IgY; D007136:Immunoglobulins