Clinical efficacy of three assays for cardiac troponin I for risk stratification in acute coronary syndromes: A thrombolysis in myocardial infarction (TIMI) 11B substudy

Background: Significant analytic variability exists between the multiple assays for cardiac troponin I (cTnI) approved for clinical use. Until adequate cTnI standardization is possible, an evidence-based approach evaluating each assay at specific thresholds appears warranted. Methods: We examined the efficacy of three cTnI assays for predicting death, myocardial infarction (MI), or the composite of death, MI, or urgent revascularization at 43 days among patients with non-ST-elevation acute coronary syndromes enrolled in the Thrombolysis In Myocardial Infarction (TIMI) 11B study. Results: Six hundred eighty-one patients with serum samples obtained at baseline and/or 12-24 h had cTnI determined using all three assays. Baseline cTnI was greater than or equal to 0.1 mu g/L for 368, 395, and 418 patients with the Bayer Immune 1(TM), ACS:180(R), and Dimension(R) RxL assays, respectively. Correlation coefficients for the RxL with the ACS:180 and Bayer Immune 1 results were 0.89 (P = 0.0001) and 0.87 (P = 0.0001), with a coefficient of 0.92 (P = 0.0001) for the ACS:180 and Bayer Immuno 1 assays. Patients with cTnI greater than or equal to 0.1 mu g/L were at increased risk for death or MI by 43 days (relative risk, 2.2-3.0; P < 0.0006), regardless of the assay used. This prognostic capacity persisted among those with creatine kinase MB isoenzyme concentrations within the reference interval. Moreover, cTnI was the strongest multivariate predictor of death, MI, or urgent revascularization with adjusted odds ratios of 2.1-2.9 (P < 0.0006). Conclusion: This study demonstrates the prognostic efficacy of three independently developed cTnI assays at a threshold of 0.1 mu g/L for the prediction of adverse clinical outcomes among patients with non-ST-elevation acute coronary syndromes. (C) 2000 American Association for Clinical Chemistry.