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.