Minor elevations in troponin T values enhance risk assessment in emergency department patients with suspected myocardial ischemia: analysis of novel troponin T cut-off values

BACKGROUND: A consensus document developed by a joint committee of the European Society of Cardiology and the American College of Cardiology redefines myocardial infarction (MI) using an increase of troponin I or T as compared to a reference control population (i.e., troponin T (TnT) of 0.01 microg/l). A clinical problem arises when an arbitrary cut-off point is selected for determination of MI (i.e., TnT> or =0.1 microg/l), as minor elevations of troponin are associated with increased cardiovascular risk in selected patients with acute coronary syndromes.

METHODS: We prospectively studied 420 unselected patients being evaluated for suspected myocardial ischemia in the emergency department (ED). We compared a 99th percentile MI cut-off limit for TnT, determined by constructing a standard receiver operator curve from our ED population in whom an acute coronary syndrome was excluded, to a standard MI cut-off limit of 0.1 microg/l in assessing cardiovascular risk. We also assessed the prognostic value of detectable TnT concentrations below this 99th percentile MI cut-off, but above the upper reference limit of healthy controls.

RESULTS: The diagnosis of acute coronary syndromes (ACS) was more frequent in groups with higher TnT concentrations: 16.8% with a normal TnT (<0.03 microg/l), 29.5% with detectable TnT below the 99th percentile MI limit (0.03-0.066 microg/l), 64.3% with detectable TnT between the 99th percentile and standard MI cut-offs (0.067-0.099 microg/l), and 85.4% with TnT> or =0.1 microg/l (p<0.001 for the trend). Thirty-day cardiovascular event rates increased for any detectable concentration of troponin: 1.3% with normal TnT, 4.8% with detectable TnT below the 99th percentile MI limit, 15.4% with TnT between the 99th percentile and standard MI cut-off limits, and 12.5% with TnT> or =0.1 microg/l (p<0.01 for the trend).

CONCLUSION: Using an MI cut-off concentration for TnT from a "non-ACS reference" improves risk stratification, but fails to detect a positive TnT in 11.7% of subjects with an acute coronary syndrome.