Comparison of cardiovascular prognosis by 3 serum cystatin C methods in the Heart and Soul Study.

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.