Troponin Limit of Detection Plus Cardiac Risk Stratification Scores to Rule Out Acute Myocardial Infarction and 30-Day Major Adverse Cardiac Events in ED Patients

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When screening for acute myocardial infarction (AMI), troponin levels below the 99th percentile, including those below the limit of detection (LOD), are considered normal. We hypothesized that a low-risk HEART score (0–3) or ACS Pretest Probability Assessment <2% plus a single troponin below the LOD would rule out both AMI and 30-day major adverse cardiac events (MACE). We studied all patients who presented to a single academic emergency department and received a troponin I (Siemens Ultra Troponin I) from September 1, 2013, to November 13, 2013 (n=888). Demographic and clinical data were abstracted from the electronic medical record. Primary outcome was a final encounter diagnosis of myocardial infarction. Secondary outcome was 30-day MACE, defined as composite of myocardial infarction, revascularization, or death from a cardiac or uncertain etiology. Sensitivities of low-risk HEART score and ACS Pretest Probability <2% alone were 98% (95% confidence interval [CI], 89%–100%) and 96% (95% CI, 86%–100%) for AMI and 94% (95% CI, 86%–98%) and 95% (95% CI, 88%–99%), respectively, for 30-day MACE. When combined with troponin below the LOD, sensitivity for AMI was 100% (95% CI, 93%–100%; difference 2%; 95% CI, −2% to 6%) for low-risk HEART Score and 100% (95% CI, 93%–100%; difference 4%; 95% CI, −1.5% to 10%) for ACS Pretest Probability <2%. When combined with troponin below the LOD, sensitivity for 30-day MACE was 100% (95% CI, 95%–100%; difference 6%; 95% CI, 1%–12%) for low-risk HEART Score and 100% (95% CI, 95%–100%; difference 5%; 95% CI, 0.2%–10%) for ACS Pretest Probability <2%. Addition of a single troponin below the LOD to these scores improves sensitivity for 30-day MACE.

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