Suspected myocardial infarction in the emergency department : An evaluation of clinical thresholds for the Beckman Coulter Access hsTnI high-sensitivity cardiac troponin I assay

Objective
The primary objective was to determine rapid rule-out (RRO) criteria for the outcome of myocardial infarction (MI) using the Beckman Coulter Access high-sensitivity cardiac troponin I (hs-cTnI) assay. Secondary objectives were to explore cut-points for rapid rule-in (RRI) and amount of change at 3-h (3-h delta) indicative of MI.

Methods
A retrospective study included ED patients with suspected MI between June and September 2019. hs-cTnI levels were performed at baseline and after 3 h. The performance benchmark for RRO criteria was a negative predictive value (NPV) for MI with a lower 95% confidence limit >99%, and for RRI and 3-h delta cut-points was a positive predictive value (PPV) for MI >70%. Delta calculation required rising hs-cTnI levels, with at least one above the 99th percentile of the upper reference limit. Analyses utilised receiver operating characteristic (ROC) curves and contingency tables.

Results
Baseline hs-cTnI levels from 935 patients were available for RRO analyses. Of tested criteria, baseline hs-cTnI <6 ng/L (females) or <11 ng/L (males) plus symptom onset >2 h met the performance benchmark (NPV: 100% [95% confidence interval 99–100]). hs-cTnI levels were available for RRI and 3-h delta analyses from 935 and 52 patients, respectively. A 3-h delta cut-point >35 ng/L met the performance benchmark (PPV: 81% [95% confidence interval 58–95]) but no RRI cut-point did so.

Conclusions
For the Beckman Coulter Access hs-cTnI assay, RRO criteria of baseline hs-cTnI <6 ng/L (females) or <11 ng/L (males) plus symptom onset >2 h met our performance benchmark. A 3-h delta cut-point >35 ng/L met the performance benchmark, but poor precision means further adequately powered research is required.

© 2023 The Authors. Emergency Medicine Australasia published by John Wiley & Sons Australia, Ltd on behalf of Australasian College for Emergency Medicine.

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