TESTING TRENDS

High-Sensitivity Troponin Test Rules Out Heart Attacks Faster

Use of a high-sensitivity cardiac troponin test (hs-cTnT) may be able to more quickly determine whether emergency department patients are having a heart attack, according to a research letter published in Circulation. The authors say that a new protocol for rapid rule-out of myocardial infarction using the hs-cTnT assay ruled out more than half of all patients within one hour.

Cardiac troponin is released into the bloodstream following damage to the heart. Traditional cTnT tests measure troponin levels at presentation to the emergency department and then three hours later. The rapid, hs-cTnT tests have been used in Europe for years, but are only entering clinical practice in the United States. There had been concern that adoption of hs-cTnT would result in an “unmanageable burden” of abnormal cardiac troponin results.

Researchers from University of Texas Southwestern Medical Center developed a novel hs-cTnT protocol, including the addition of a three-hour hs-cTnT measurement for patients classified as indeterminate at one hour. The proportion of patients eligible for early rule-out with the new protocol using hs-cTnT was compared to conventional fourth-generation, three-hour cTnT assays. cTnT and hs-cTnT were measured at 0, 1, and 3 hours after presentation in 536 patients with symptoms suggestive of MI (August to October 2017).

Based on hs-cTnT results, individuals were classified into two categories, “ruled out” or “abnormal.” Using the conventional assay, patients were ruled out if cTnT was <0.01 ng/mL at all time points and abnormal if any value was ≥ 0.01 ng/mL. Three cardiologists adjudicated final diagnosis based on all available clinical information.

Three hs-cTnT assays have received clearance from the U.S. Food and Drug Administration

  • January 2017: Roche’s Elecsys Troponin T Gen 5 Stat blood test for use on cobas analyzers.
  • July 2018: Siemens Healthineers’ high-sensitivity troponin I assays for the Atellica IM and ADVIA Centaur XP/XPT in vitro diagnostic analyzers.

  • June 2018: Beckman Coulter Diagnostics’ Access hsTnI, for use on the Access 2, DxI, and the Access family of immunoassay systems.

Using the conventional assay, the researchers ruled out 80.4 percent of patients at three hours. Using the new hs-cTnT protocol, 83.8 percent ruled out by 3 hours, including 30.0 percent at baseline, 24.8 percent at 1 hour, and 28.9 percent at 3 hours. Significantly fewer patients were classified as abnormal using the new protocol versus the conventional assay (16.2 percent versus 19.6 percent). The new protocol had a sensitivity and negative predictive value of 100 percent, specificity of 86 percent, and positive predictive value of 13 percent for a final adjudicated diagnosis of MI. Among patients who ruled out, there were no recurrent MI events reported over 30 days of follow-up.

“The positive predictive value of an abnormal hs-cTnT value was notably lower in this population than in prior studies, reflecting similar specificity applied to a population with much lower MI prevalence,” write the authors led by Rebecca Vigen, M.D., from University of Texas Southwestern Medical Center in Dallas. “Thus, clinical judgment remains essential in the interpretation of abnormal troponin values as the hs- cTnT assay becomes adopted in the United States, where troponin is measured more indiscriminately than in many other countries.”

Takeaway: hs-cTnT can rule out heart attacks faster in the emergency department than conventional assays, seemingly allaying concerns of a larger burden of abnormal results. This next generation of sensitive tests appears poised for clinical adoption in the United States.

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