Evaluation of High-Sensitivity Cardiac Troponin I Levels in Patients With Suspected Acute Coronary Syndrome.

Importance: Low concentrations of high-sensitivity cardiac troponin I determined on presentation to the emergency department (ED) have been shown to have an excellent negative predictive value (NPV) for the identification of acute myocardial infarction. The sensitivity, and therefore clinical applicability, of such testing strategies is unknown.
Objective: To determine the diagnostic performance of low concentrations of high-sensitivity cardiac troponin I in patients with suspected cardiac chest pain and an electrocardiogram showing no ischemia as an indicator of acute myocardial infarction.
Design, Setting, and Participants: A pooled analysis of 5 international (Australia, New Zealand, and England) prospective, observational cohort studies with blinded outcome assessment and 30-day follow-up was conducted. A total of 3155 patients presenting with symptoms suggestive of cardiac ischemia were included in the analysis. Eligible patients had a nonischemic electrocardiogram determined and high-sensitivity troponin I measured at presentation. The lower limit of detection (1.2 ng/L) as well as cutoff concentrations rounded to the nearest integer for a high-sensitivity troponin I assay were used in the analysis. Recruitment was undertaken from November 1, 2007, to August 10, 2013.
Main Outcomes and Measures: The primary outcome was fatal or nonfatal acute myocardial infarction occurring within 30 days of ED presentation, adjudicated with serial troponin testing. The secondary outcome was the proportion of patients potentially suitable for early discharge at each cutoff concentration.
Results: Of the 3155 eligible patients, 1771 were male (56.1%), and mean (SD) age was 57.4 (13.3) years. Acute myocardial infarction developed in 291 individuals (9.2%). The 1.2-ng/L limit of detection gave a sensitivity of 99.0% (95% CI, 96.8%-99.7%) and an NPV of 99.5% (95% CI, 98.4%-99.9%). This cutoff level would allow for early discharge of 594 patients (18.8%). All higher rounded cutoff values had sensitivities less than 98.0%. Diagnostic performance of the limit of detection was maintained when patients were stratified by age, sex, risk factors, presence of coronary artery disease, and early presentation.
Conclusions and Relevance: High-sensitivity troponin I concentrations determined at presentation to the ED that were below the limit of detection identified 18.8% of patients potentially suitable for discharge, with a high sensitivity for acute myocardial infarction. Rounded cutoff values above the limit of detection may not have the required sensitivity for clinical implementation.