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High-sensitivity troponin I protocols to identify myocardial infarction from the first measurement at admission do best with the lowest diagnostic thresholds, a study showed, while another reaffirmed that faster serial measurement protocols are safe.

In pooled analysis of five prospective emergency department cohort studies from Australia, New Zealand, and England, an initial high sensitivity-troponin I result coming in below the limit of detection -- less than 1.2 ng/L -- had a .

Other cutoffs for the same assay weren't up to the criterion of missing no more than 1% of MI events, Edward Carlton, PhD, of Southmead Hospital in Bristol, England, and colleagues reported online in JAMA Cardiology.

The single measurement at presentation strategy wasn't quite as accurate for early presenters, arriving within 2 hours of onset. The sensitivity, even at 1.2 ng/L, was 98.6%.

The pooled analysis included 3,155 patients, among whom 9.2% had an MI and 33.5% presented less than 2 hours after symptom onset.

The second study released alongside in JAMA Cardiology affirmed that serial use of the high-sensitivity test at presentation and at 1 hour was "comparable" in performance to a 3-hour protocol, as had been initially reported at the European Society of Cardiology meeting.

"With application of a low troponin I cutoff value of 6 ng/L, the rule-out algorithm showed a after 1 hour for non–ST-segment elevation MI type 1," , of the University Heart Center Hamburg, Germany, and colleagues reported. "Similarly, a rule-in algorithm based on troponin I levels provided a high positive predictive value with 82.8% (95% CI 73.2%-90.0%)."

Again, a lower cutoff appeared better, the researchers wrote, as "application of the cutoff of 6 ng/L resulted in lower follow-up mortality (1.0%) compared with the routinely used 99th percentile (3.7%) for this assay."

Their prospective Biomarkers in Acute Cardiac Care (BACC) study included 1,040 patients presenting to the emergency department with acute chest pain from July 19, 2013, to Dec. 31, 2014, along with two independent cohorts totalling 4,009 patients.

High-sensitivity troponin tests are used routinely in many regions of the world but haven't yet become available in the U.S., , of Brigham and Women's Hospital in Boston, noted in .

Despite frustration with the increasing proportion of patients with elevated troponin levels by the more sensitive tests who ultimately get non-MI diagnoses, rapid triage of chest pain in the emergency department is likely to be an application embraced by practitioners, Morrow noted.

"There is a need for additional studies performed in diverse health care settings, including in the United States, to add to the robustness of the estimated negative predictive value across a variety of populations," the editorial concluded. "At present, because high-sensitivity troponin assays are not available in the United States, serial testing at presentation and 3 to 6 hours with a contemporary sensitive assay remains the U.S. standard of care."