Zero-hour thresholds to risk stratify patients for acute myocardial infarction using a point-of-care high-sensitivity troponin assay

AIMS: High-sensitivity cardiac troponin (hs-cTn) assays are crucial in assessing suspected myocardial infarction (MI). International recommendations recommend evaluating new assays to identify metrics for clinical use. Our primary aim was to identify patients at low risk of index MI using a point of care hs-cTnI (Abbott i-STAT® hs-TnI) assay at presentation. We also sought to examine the diagnostic accuracy of a single value for identifying patients at high risk for acute MI. METHODS AND RESULTS: This prospective multicentre observational trial enrolled patients with suspected acute coronary syndrome. Nine hundred sixty-seven patients had blood drawn on presentation to the emergency department for hs-cTnI measurement. The primary outcome was index MI including type one or two non-ST segment elevation MI. Diagnostic accuracy statistics were calculated at a range of hs-cTnI values. 5.6% of patients met the criteria for MI. A cut-off <8 ng/L was the highest threshold to achieve an negative predictive value >99.5%. This threshold had a sensitivity of 94.4% (95% CI: 84.6-98.8%). An hs-cTnI concentration of <5 ng/L provided a sensitivity of 100% (95% CI: 93.4-100.0%). For identifying high-risk patients, the positive predictive value (PPV) is the highest at a troponin of >60 ng/L (68.3%, 95% CI: 51.9-81.9%). A PPV of 50% (95% CI: 38.0-62.0%) is achieved at a cut-off of >25 ng/L. CONCLUSION: This study identified two hs-cTnI thresholds (<5 ng/L or <8 ng/L) to identify patients at low risk and two thresholds (>25 ng/L and >60 ng/L) to identify patients at high risk for MI. Our findings provide promise for improving care in rural and inner-city medical settings.