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

Background and 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 (POC) 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 AMI.

Methods: This prospective multi-centre observational trial enrolled patients with suspected acute coronary syndrome. 967 patients had blood drawn on presentation to the ED for hs-cTnI measurement. The primary outcome was index MI including type one or two non-ST segment elevation MI (NSTEMI). Diagnostic accuracy statistics were calculated at a range of hs-cTnI values.

Results: 5.6% of patients met the criteria for MI. A cutoff of <8 ng/L was the highest threshold to achieve an NPV >99.5%. This threshold had a sensitivity of 94.4% (95% CI: 84.6-98.8%). A hs-cTnI concentration of <5ng/L provided a sensitivity of 100% (95% CI: 93.4% to 100.0%). For identifying high-risk patients, the PPV is highest at a troponin of >60ng/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.

Conclusions: This study identified two hs-cTnI thresholds (<5ng/L or <8ng/L) to identify patients at low risk and two thresholds (>25ng/L and >60ng/L) to identify patients at high risk for MI. Our findings provide promise for improving care in rural and inner-city medical settings.