Abstract 8905: Cardiac Troponin Thresholds and Kinetics to Differentiate Myocardial Injury and Myocardial Infarction

Abstract

Background: Whilst the 99th percentile is the recommended diagnostic threshold for myocardial infarction (MI), some guidelines also advocate the use of higher troponin thresholds to rule-in MI at presentation. It is unclear whether the magnitude or change in troponin concentration can differentiate causes of myocardial injury and infarction in practice. Hypothesis: Troponin concentration alone cannot to distinguish subtypes of myocardial infarction Methods: In a secondary analysis of a multi-centre randomized controlled trial, we identified 46,092 consecutive patients presenting with suspected acute coronary syndrome without STEMI. High-sensitivity troponin I concentrations at presentation and on serial testing were evaluated. The positive predictive value (PPV) and specificity were determined at the sex-specific 99th percentile upper reference limit (URL), and rule-in thresholds of 64 ng/L and 5-fold of the URL for a diagnosis of type 1 MI. Results: Troponin concentrations were similar at presentation in type 1 (median [IQR] 91 [30-493] ng/L) and type 2 MI (50 [22-147] ng/L), and in acute (50 [26-134] ng/L) and chronic (51 [31-130] ng/L) myocardial injury (Figure A). The 99th percentile and rule-in thresholds of 64 ng/L and 5-fold URL gave a PPV of 57% (95% confidence interval [CI] 56-58%), 59% (58-61%) and 62% (60-64%), and a specificity of 96% (96-96%), 96% (96-96%) and 98% (97-98%), respectively (Figure B). The absolute, relative and rate of change in troponin concentration was highest in patients with type 1 MI (P<0.001 for all, Figure C). Discrimination improved when troponin concentration and change in troponin were combined compared to troponin concentration at presentation alone (area under curve, 0.661 versus 0.613). Conclusions: Troponin concentrations at presentation are insufficient to distinguish type 1 MI from other causes of myocardial injury or infarction in practice and should not guide management decisions in isolation.