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Prior research has indicated that myocardial infarction (MI) can be ruled out safely based on 0- and 3-hour troponin testing (NEJM Journal Watch Emerg Med Feb 2012 and JAMA 2011; 306:2684). In a new, multinational observational study, investigators evaluated the ability of high-sensitivity troponin T (hsTnT) levels at 0 and 1 hour to indicate appropriate dispositions.
If the hsTnT level was below 12 ng/L initially and increased by less than 3 ng/L after 1 hour, the patient was considered “ruled out” for MI. Final diagnoses were determined by two independent cardiologists who relied on all available information except the hsTnT result, to which they were blinded.
Among 1282 patients, MI was ruled out in 813 (63%). Of these, 7 were diagnosed with MI, for a negative predictive value of 99.1%. Positive predictive value was 77.2%, specificity 96.1%.
Mueller C et al. Multicenter evaluation of a 0-hour/1-hour algorithm in the diagnosis of myocardial infarction with high-sensitivity cardiac troponin T. Ann Emerg Med 2016 Jan 12; [e-pub]. (http://dx.doi.org/10.1016/j.annemergmed.2015.11.013)
Comment
In patients with chest pain, if the hsTnT level is below 12 ng/L initially and increases by less than 3 ng/L after 1 hour, MI is ruled out by this algorithm. But given its negative predictive value of 99.1%, for every 1000 patients you discharge, 9 will ultimately rule in. That means we cannot rely on troponin in isolation, but must also make sure the patient is otherwise low risk (i.e., normal or unchanged electrocardiogram and atypical symptoms). Lastly, don't forget important alternate diagnoses such as aortic dissection and pulmonary embolism.