High-sensitivity troponin and the application of risk stratification thresholds in patients with suspected acute coronary syndrome

Background: Guidelines acknowledge the emerging role of high-sensitivity cardiac troponin for risk stratification and the early rule-out of myocardial infarction, but multiple thresholds have been described. We evaluate the safety and effectiveness of risk stratification thresholds in patients with suspected acute coronary syndrome.
Methods: Consecutive patients with suspected acute coronary syndrome (n=48,282) were enrolled in a multi-center trial across ten hospitals in Scotland. In a prespecified secondary and observational analysis, we compared the performance of the limit of detection (<2 ng/L) and an optimised risk stratification threshold (<5 ng/L) using the Abbott high sensitive troponin I assay. Patients with myocardial injury at presentation, with ≤ 2 hours of symptoms or with ST-segment elevation myocardial infarction were excluded. The negative predictive value (NPV) was determined in all patients and in subgroups for a primary outcome of myocardial infarction or cardiac death within 30 days. The secondary outcome was myocardial infarction or cardiac death at 12 months, with risk modelled using logistic regression adjusted for age and sex.
Results: In total, 32,837 consecutive patients (61±17 years, 47% female) were included, of whom 23,260 (71%) and 12,716 (39%) had cardiac troponin I concentrations <5 ng/L and <2 ng/L at presentation. The NPV for the primary outcome was 99.8% (95% confidence interval [CI] 99.7-99.8%) and 99.9% (95% CI 99.8-99.9%) in those with cardiac troponin I concentrations <5 ng/L and <2 ng/L, respectively. At both thresholds, the NPV was consistent in men and women and across all age groups, although the proportion of patients identified as lowrisk fell with increasing age. Compared to patients with cardiac troponin I concentrations ≥5ng/L but <99th centile, the risk of myocardial infarction or cardiac death at 12 months was 77% lower in those <5 ng/L (5.3% versus 0.7%; adjusted Odds Ratio [aOR] 0.23, 95% CI 0.19-0.28), and 80% lower in those <2 ng/L (5.3% versus 0.3%; aOR 0.20, 95% CI 0.14-0.29).
Conclusions: Use of risk stratification thresholds for high-sensitivity cardiac troponin I identify patients with suspected acute coronary syndrome and at least 2 hours of symptoms as low-risk at presentation irrespective of age and sex.
Clinical Trial Registation: URL: https://clinicaltrials.gov Unique Identifier: NCT01852123.