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High-Sensitivity Troponin Tests Have Hospitals Adjusting to Increase in Positive Results


NEW YORK (360Dx) – At Mayo Clinic in Rochester, Minnesota, the number of elevated troponin readings in the emergency room nearly doubled when the hospital began using Roche's Elecsys Troponin T Gen 5 Stat test, a high-sensitivity troponin T test, according to Allan Jaffe, chair of the division of clinical core laboratory services in the department of laboratory medicine and pathology at Mayo Clinic.

"We were prepared for that," Jaffe said. "We knew that was going to happen because we did a pilot study. We spent many months working on it and making sure everyone understood what was going to happen."

With new high-sensitivity tests hitting the market, sharp increases in elevated troponin test results, such as Mayo Clinic experienced, had been anticipated by laboratorians, but for clinical staff at hospitals, adjusting to how to interpret those results have, nonetheless, been a work in progress, so far.

In January 2017, Roche's Elecsys Troponin T Gen 5 test became the first high-sensitivity troponin test to be cleared for marketing in the US by the Food and Drug Administration. Since then, other tests have also received 510(k) clearance by the agency, including tests from Beckman Coulter Diagnostics and from Siemens Healthineers.

With these new tests, "People have to get used to the fact that they are going to see many more positive results than they ever saw before with the conventional assays," said Alan Wu, chief of the clinical chemistry and toxicology laboratories at San Francisco General Hospital and professor of laboratory medicine at University of California-San Francisco. "They have to understand what that means. It doesn't necessarily rule-in for acute coronary syndromes, it just indicates cardiac injury."

Particularly with older, less sensitive assays, many clinicians used troponin to help confirm diagnosis of ischemic heart disease, Mayo Clinic's Jaffe noted. As a result, some clinicians may now need to become more familiar with new high-sensitivity assays to better understand how to interpret the results.

"In fairness, with older assays, it took higher values before you saw an elevation, so a greater percentage of them were due to ischemic heart disease," Jaffe said. "So yes, it is an issue that every time some people see an elevated troponin, their inclination is to say that it has to be ischemic heart disease. That is not correct. The vast majority of the increases in troponin that are seen with higher-sensitivity assays are not due to ischemic heart disease."

One concern is that clinicians may misinterpret the lower level troponin increases identified by the high sensitivity tests as fast positives, Wu said.

"Consistently the literature has shown that any increases in troponin above the 99th percentile, irrespective of the ideology, portends to adverse cardiac risk in the future," Wu said. "So those are not false positive results, they are true positives for cardiac injury."

Some facilities may have a steeper adjustment to the new assays than others, depending on the cutoffs that were being used to read results of their previous assays. Practice recommendations for the use of high-sensitivity troponin published last spring by the American Association of Clinical Chemistry recommended using the 99th percentile as a cutoff point for measuring troponin, meaning above the 99th percentile is considered elevated. While the 99th percentile level is part of the universal definition of myocardial infarction and has been recommended for years, not all laboratories adopted it. Many laboratories used even higher cutoffs, Wu and Jaffe noted.

"If you were using the 99th percentile, then you would have less sticker shock than if your local laboratory was not using it. [For facilities using higher cutoffs] you are talking about not only an increase in sensitivity due to the assay, but an increase in sensitivity just due to the fact that the cutoff value that is being used has now moved from inappropriate to appropriate," Jaffe said.

There are indications that the new higher sensitive assays may also shorten the time to diagnosis. Troponin, which is measured over a series of time intervals, is typically measured at intervals of zero, four and eight hours, or zero, three and six hours, according to Wu.

"We are seeing increasingly zero, two and four [hours], and in some cases even zero and one [hour], so the time intervals are declining and the number of samples are decreasing as we go to high sensitivity," Wu said.

A University of Texas study of 536 patients published in the journal Circulation found that Roche's high-sensitivity assay was able to rule out myocardial infarction in half of patients within an hour.

The shortened time frames are due to the fact that lower troponin elevations, which may have registered as zeros on previous assays, are now measurable, according to Wu.

"You can't measure a delta change if it goes from zero to zero. Now, with more patients we have a measureable value," he said.

The new high-sensitivity assays also have different reporting units. While troponin is measured in nanograms per milliliter, the AACC practice recommendations recommended that high-sensitivity assays be reported in nanograms per liter. The change means high-sensitivity troponin test results are reported in whole numbers rather than decimal point fractions.

While the new numbers should be easier to understand, for hospitals changing to high-sensitivity assays it will be critical that everyone is made aware of the change, Wu said. This can be particularly challenging in departments that might have multiple shifts or relatively transient staff, he said.

"We are still in the process of validating our high-sensitivity troponin assay, but on the day that we turn it on, I will be in the emergency department and I will be talking to the people on the floors as the results are coming through," to ensure they understand the new whole number values, he said.

At Mayo, Jaffe said that the new reporting units were quickly adopted and not problematic. His bigger concern is that clinicians look at the big picture in evaluating results.

"The best results come from incorporating the assay results into the clinical picture," he said. "Some clinicians believe that the values are the be all and end all. What they ought to be saying is, my clinical impression is the end-all, and the lab simply helps me to consolidate and confirm my diagnosis."