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 estimate glomerular filtration (eGFR). 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 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.

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