High-Sensitivity Cardiac Troponin I Levels in ACS Patients
What is the diagnostic performance of low concentrations of high-sensitivity cardiac troponin I (hs-cTnI) in patients with suspected cardiac chest pain and an electrocardiogram (ECG) showing no ischemia as an indicator of acute myocardial infarction (AMI)?
A pooled analysis of five international (Australia, New Zealand, and England) prospective, observational cohort studies with blinded outcome assessment and 30-day follow-up was conducted. A total of 3,155 patients presenting with symptoms suggestive of cardiac ischemia were included in the analysis. Eligible patients had a nonischemic ECG determined and hs-TnI measured at presentation. The lower limit of detection (1.2 ng/L) as well as cutoff concentrations rounded to the nearest integer for a hs-TnI assay were used in the analysis. The primary outcome was fatal or nonfatal AMI occurring within 30 days of emergency department (ED) presentation, adjudicated with serial troponin testing. The secondary outcome was the proportion of patients potentially suitable for early discharge at each cutoff concentration.
Of the 3,155 eligible patients, 1,771 were male (56.1%), and mean (standard deviation) age was 57.4 (13.3) years. AMI developed in 291 individuals (9.2%). The 1.2-ng/L limit of detection gave a sensitivity of 99.0% (95% confidence interval [CI], 96.8%-99.7%) and a negative predictive value of 99.5% (95% CI, 98.4%-99.9%). This cut-off level would allow for early discharge of 594 patients (18.8%). All higher rounded cut-off values had sensitivities <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.
The authors concluded that hs-TnI 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 AMI.
This study reports that hs-TnI concentrations determined at presentation to the ED that were below the limit of detection identified approximately 19% of patients potentially suitable for discharge with a high sensitivity for AMI. However, rounded cutoff values above the limit of detection may not have the required sensitivity for clinical implementation. These findings can be applied only to the assay tested (hs-cTnI) and cannot be translated to other assays, even high-sensitivity ones. Furthermore, no hs-cTn assay is currently approved for use by the Food and Drug Administration, and whether the use of low concentrations of hs-cTn in clinical practice will be approved remains unknown.
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