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Clinical Performance of Newer, More-Sensitive Troponin Assays

The new assays improve early detection of MI.

Currently available troponin assays are not sufficiently sensitive immediately after the onset of chest pain because they do not reliably detect very low levels of troponin; use of these assays might deprive patients without ST-segment elevation of the benefits of early intervention. In two prospective, multicenter, observational studies, researchers evaluated the diagnostic accuracy of newer, more-sensitive troponin assays for identifying myocardial infarction in patients who presented to emergency departments with chest pain. In both studies, cardiologists independently determined the final diagnoses using hospital records.

Reichlin and colleagues, in a partially industry-funded study, compared standard troponin T testing against four new troponin T and I assays in 718 patients at presentation and at 1, 2, 3, and 6 hours after. Patients with renal failure who required dialysis were excluded. The four new assays were each significantly more sensitive for identifying MI than the standard assay at all time points and were similarly sensitive to each other. For example, at presentation, the area under the receiver-operating characteristic curve was 0.94 or 0.96 for the new tests versus 0.90 for the standard assay. The increased sensitivity was most marked in the subset of patients who presented within 3 hours of symptom onset (area under the receiver-operating characteristic curve, 0.92–0.94 vs. 0.76). Test performance was not affected by renal dysfunction. Diagnostic accuracy of the new tests for detecting unstable angina was low to moderate (range of negative predictive values, 74% to 82%).

Keller and colleagues compared a single new troponin I assay with standard troponin T testing in 1818 patients at presentation and at 3 and 6 hours after. The new assay was more sensitive for identifying MI than the current standard (e.g., at presentation, 90.7% vs. 72.7%) and was markedly more sensitive in the subset of patients who presented within 3 hours of onset of chest pain (84.0% vs. 55.2%). To distinguish ischemic causes from other causes of troponin elevation, the researchers expanded the definition of MI to include a troponin rise or fall of at least 30% within 6 hours of presentation. Use of the expanded definition allowed detection of 100% of MIs within 3 hours of presentation.

Comment: These newer, more-sensitive troponin assays will allow earlier detection (or exclusion) of MI, but whether they will improve patient outcomes remains to be seen. With the new assays, as with current assays, sensitivity for unstable angina is inadequate, and discharging a patient after a single troponin test remains imprudent.

— J. Stephen Bohan, MD, MS, FACP, FACEP

Published in Journal Watch Emergency Medicine August 26, 2009

Citation(s):

Reichlin T et al. Early diagnosis of myocardial infarction with sensitive cardiac troponin assays. N Engl J Med 2009 Aug 27; 361:858.

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• Medline abstract (Free)

Keller T et al. Sensitive troponin I assay in early diagnosis of acute myocardial infarction. N Engl J Med 2009 Aug 27; 361:868.

• Original article (Subscription may be required)
• Medline abstract (Free)

Morrow DA. Clinical application of sensitive troponin assays. N Engl J Med 2009 Aug 27; 361:913.

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• Medline abstract (Free)