Stressing the Utility of High-Sensitivity Cardiac Troponin Testing in Patients with Possible Cardiac Ischemia

Strategies to rule out myocardial infarction (MI)2 in the emergency department include stress test echocardiography, electrocardiography, and assessment of cardiac biomarkers such as troponin I and T (1). The potential for new high-sensitivity cardiac troponin testing to simplify and expedite these rule-out protocols is of great interest. Is all the hype justified? Or are we placing unreasonable expectations on a single laboratory test? There are indeed data indicating that an undetectable or low high-sensitivity cardiac troponin concentration alone at presentation might be useful to rule out MI. Recent data, however, suggest that the addition of other tests may improve the performance and be even more cost-effective compared to high-sensitivity cardiac troponin alone (2, 3). As a laboratory professional, this is welcome news as one has to wonder if the amount of stress placed on a single test, at a single time point, at such low concentrations imposes unrealistic expectations on the test performance (4). Ruling out MI, after all, is only one of the many conditions that physicians are concerned about when patients present with symptoms suggestive of acute coronary syndrome (ACS). In fact, if highsensitivity cardiac troponin alone is not sufficient for ruling-out MI among patients with ACS, is there any utility for this test in ruling-out or ruling-in cardiac ischemia? In this issue of JALM, Limkakeng et al. (5) explore this topic bymeasuring high-sensitivity cardiac troponin T (hs-cTnT) before and 2 h after an exercise stress test in a well-characterized population suspected of having ACS, with cTnT (4th generation) <100 ng/L before the stress test. In their study population of 317 patients, only 26 patients (8%) were positive for ischemia by exercise stress echocardiography, and there were only 8 patients who had a composite cardiac outcome (i.e., any revascularization, MI, or death) within 90 days of the index visit (5). Three major findings from this work are evident: (a) patients with exercise stress– induced cardiac ischemia had higher baseline and 2-h concentrations of cTnT (4th generation) than patients without ischemia, but the majority of patients with ischemia had hs-cTnT concentrations below 14 ng/L (99th percentile cutoff); (b) the change in hs-cTnT concentrations frombaseline to 2 h after the stress test was not significant in either group; (c) using the limit of the blank (i.e., hs-cTnT <3 ng/L) at baseline to rule out ischemia would miss 8 patients (or 30% of the 26 patients) who were positive for cardiac ischemia and would miss 2 patients (or 25% of the 8 patients) who had a composite cardiac outcome at 90 days (5).