title: Comparison of cardiovascular prognosis by 3 serum cystatin C methods in the Heart and Soul Study.
abstract: BACKGROUND
  Cystatin C is a promising new biomarker to determine the estimated glomerular filtration. However, the Siemens' cystatin C assay (Siemens), used in many longitudinal studies, has had limited clinical applicability because it requires a specific, dedicated instrument. Other companies, including Gentian and Roche, have developed cystatin C assays that can be used with most routine clinical chemistry analyzers.
  
  
  METHODS
  We compared the agreement of Gentian and Roche with Siemens assays in 948 participants at the baseline visit of the Heart and Soul Study, a cohort of participants with established coronary artery disease who were followed for an average of 8 years. We then compared associations of all 3 cystatin C measures and eGFR-Modification of Diet in Renal Disease (MDRD) with clinical outcomes.
  
  
  RESULTS
  The Gentian assay had higher correlation with Siemens (r = 0.96) than did Roche (r = 0.93, P < 0.001). After cross-tabulating quartiles of each cystatin C measure, agreements (κ statistic) were higher for Siemens and Gentian (0.73, 95% CI 0.72-0.75) than for Roche and Siemens (0.64, 0.63-0.66) or for Roche and Gentian (0.69, 0.65-0.71). These differences in agreement had minimal impact on associations with clinical outcomes; the hazard ratios (HRs) for mortality comparing the high vs low quartiles were 3.2 (95% CI 2.1-4.8) for Siemens, 3.1 (CI 2.1-4.7) for Gentian, 3.1 (CI 2.1-4.7) for Roche, and 1.6 (CI 1.1-2.3) for eGFR-MDRD, after multivariate adjustment.
  
  
  CONCLUSIONS
  In summary, agreement with the Siemens' assay was modestly higher for the Gentian compared with the Roche assay, although all 3 methods for cystatin C measurement had similar utility as predictors of clinical outcomes.
authors.affiliation: San Francisco VA Medical Center, San Francisco, CA, USA. michael.shlipak@ucsf.edu
authors.forename: Michael G
authors.initials: MG
authors.lastname: Shlipak
authors.forename: Cristin C
authors.initials: CC
authors.lastname: Weekley
authors.forename: Yongmei
authors.initials: Y
authors.lastname: Li
authors.forename: Lars-Olof
authors.initials: LO
authors.lastname: Hansson
authors.forename: Anders
authors.initials: A
authors.lastname: Larsson
authors.forename: Mary
authors.initials: M
authors.lastname: Whooley
mesh_terms: D015415:Biomarkers / Q000097:blood; D003324:Coronary Artery Disease / Q000097:blood / Q000175:diagnosis* / Q000503:physiopathology; D055316:Cystatin C / Q000097:blood*; D006801:Humans; D007118:Immunoassay; D009391:Nephelometry and Turbidimetry; D011237:Predictive Value of Tests; D011379:Prognosis; D011446:Prospective Studies; D018570:Risk Assessment; D044967:Serum
chemical_list: D015415:Biomarkers; D055316:Cystatin C