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High-sensitivity troponin T (hs-TnT) testing is a reliable way to rule out low-risk patients presenting with suspected acute coronary syndrome (ACS), according to the first observational study of the now-FDA-approved assay in U.S. emergency departments.

Acute MI could be ruled out with a for men and women if hs-TnT fell below the cutoff of 19 ng/L upon measurement at presentation and at hour 3. Separately, a hs-TnT reading of less than 6 ng/L at either time point carried a negative predictive value of 99.4%, according to a group led by W. Frank Peacock, MD, of Houston's Ben Taub General Hospital.

This test identifies patients with less than 1% risk for MI, urgent revascularization, or death occurring within 30 days, the investigators reported online in JAMA Cardiology.

"Identifying a low-risk cohort may permit early emergency department discharge and avoid unnecessary hospitalization," the authors said. "Rapid turnaround of low-risk patients could translate into a reduction in emergency department volumes, which would benefit patients (shorter waiting times, increased satisfaction, improved outcomes, and saved costs), clinicians (decreased diagnostic ambiguity and medicolegal burden), and hospitals (by providing cost-saving benefits)."

The 19 ng/L cutoff -- the 99th percentile in the U.S., consistent with the Third Universal Definition of AMI -- was a good fit for both sexes: C-statistics were 0.952 and 0.962 and women and men, respectively, in the study.

"This cutpoint exceeds the 14 ng/L used globally and may be explained by geographically dependent cardiovascular risk," Peacock and colleagues commented. "When applied in clinical practice, the clinician must consider the similarities of their population to that used for the derivation of this cutpoint because the 99th percentile is entirely dependent on the reference study population. We also evaluated sex-specific upper reference levels (14 ng/L for women and 22 ng/L for men) and found diagnostic performance was largely unchanged."

"If the findings of Peacock et al hold true on further validation, implementation of hsTn tests could be the game changer we have been waiting for. It will provide clinicians with objective data to support early discharge of patients who are low risk," according to an by Frederick Korley, MD, PhD, of the University of Michigan Medical School in Ann Arbor.

"There are numerous potential benefits to clinical use of hsTn tests. However, we need to proceed cautiously," he urged.

Korley pointed out that of the 1,690 individuals who were eligible for the study -- of whom 335 were excluded for insufficient hs-TnT measurement -- eight got false negatives on the hs-TnT assay that were caught with current-generation troponin testing. "It is difficult to ascertain the clinical consequences of missing an MI diagnosis in these patients, because they were admitted and presumably treated for MI. It is unclear whether they would have experienced adverse cardiac events if they had been discharged home," he said.

Still, "it is unrealistic to expect that one biomarker will perfectly discriminate between patients with and without MI," he conceded. "It is likely that if other aspects of the clinical evaluation (e.g., the clinical history, cardiovascular risk factors, and electrocardiographic findings) are taken into consideration, the small proportion of MIs that are missed by the 0-hour and 3-hour hs-TnT results may be correctly diagnosed nonetheless."

The study was conducted at 15 emergency departments across the U.S. Patients with suspected ACS had blood analyzed on the fifth-generation Roche Elecsys hsTnT assay (cleared by the FDA in January). Serial blood samples were collected at hours 0, 3, 6-9, and 12-24.

A median 2.9 hours elapsed from symptom onset to presentation, then another 2.9 hours from presentation to baseline blood draw. Clinicians were blinded to hs-TnT results and made no clinical decisions based on the assay.

Those with non-ACS elevations of hs-TnT were excluded, limiting the applicability of the study's findings. In addition, investigators warned that the negative predictive value of the 19 ng/L cutoff may suffer if hs-TnT is assayed sooner than done in the present study cohort.