title: A sol particle homogeneous immunoassay for measuring serum cystatin C.
abstract: OBJECTIVE
  We have developed a sol particle immunoassay (SPIA) for measuring serum cystatin C, an endogenous marker of glomerular filtration rate (GFR).
  
  
  METHODS
  We used colloidal gold particles coated with anti-cystatin C antibodies.
  
  
  RESULTS
  The assay was linear in the range 0.2 to 8 mg/L and showed good correlation between theoretical and obtained values. The within and between-day coefficients of variation (CV) varied from 1.1 to 1.6% and 0.4 to 1.0%, respectively. Analytical recovery was 95.7 to 103.7%. No interference could be detected from bilirubin (up to 200 mg/L), hemoglobin (up to 3 g/L), chyle (up to 5,000 FTU), rheumatoid factor (up to 1,000 IU/mL) or anticoagulants. Serum samples (n = 101), from which turbidity had been removed, were measured either with our assay or with Dako Cystatin C PET kits, using a Model 7070 Hitachi automatic clinical analyzer. Comparing these two methods, the calculated linear regression equation and the correlation coefficient were y = 0.986 x -0.153 and r = 0.995, respectively.
  
  
  CONCLUSIONS
  Our new SPIA assay is a fully automated, homogeneous immunoassay that can readily be used in conjunction with various commercial analyzers that are currently available. The assay is sensitive, precise and suitable for clinical use and appears to offer advantages over other GFR markers such as creatinine.
authors.affiliation: Diagnostic Research & Development Dept., R&D Division, Nesco Company, Azwell Inc., 2-24-3, Sho, Ibarakicity Osaka, 5670806, Japan. mu-tanaka@azwell.co.jp
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Tanaka
authors.forename: Kenji
authors.initials: K
authors.lastname: Matsuo
authors.forename: Masayasu
authors.initials: M
authors.lastname: Enomoto
authors.forename: Koji
authors.initials: K
authors.lastname: Mizuno
mesh_terms: D015415:Biomarkers; D002138:Calibration; D003102:Colloids; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D005919:Glomerular Filtration Rate; D006046:Gold; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D011933:Reagent Kits, Diagnostic; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D003102:Colloids; D055316:Cystatin C; D015891:Cystatins; D011933:Reagent Kits, Diagnostic; D006046:Gold