High-Sensitivity Troponin T Safely Rules Out More MI Patients, and Faster, Than Conventional Assay

A modified algorithm using a high-sensitivity cardiac troponin T (hs-cTnT) assay safely and rapidly ruled out more patients with myocardial infarction in one US emergency department, with more than half of patients ruled out 1 hour after presentation, when compared with a conventional troponin assay, a new study shows.

The early rule out with hs-cTnT appears safe, according to investigators, with a sensitivity and negative predictive value of 100%, meaning the test did not miss any patients with MI. The positive predictive value—which is a measure of probability that a patient with an abnormal test result has the disease—was 13%, which is lower than in previous studies “but reflects similar specificity applied to a population with much lower MI prevalence,” Rebecca Vigen, MD (UT Southwestern Medical Center, Dallas, TX), and colleagues August 6, 2018, report in Circulation.

To TCTMD, senior investigator Sandeep Das, MD (UT Southwestern Medical Center), said hospital systems need to have processes of care in place in order to take of advantage of the high-sensitivity assay. In other words, simply replacing the current traditional troponin assay with the high-sensitivity test won’t make any difference unless everybody is on board.

“If you don’t make a decision until the patient has been there for 6 hours, then the type of assay you use won’t matter,” he said. “Our emergency department nurses have been fantastic about rising to the challenge of a precise 1-hour timed blood draw, and our emergency department leadership and faculty have been very willing to embrace the new process geared toward faster decision-making.”   

Since 2015, the European Society of Cardiology (ESC) has recommended the use of high-sensitivity assays for the diagnosis of MI. The ESC guidelines recommend a 0/1-hour algorithm for patients with suspected NSTEMI using high-sensitivity cardiac troponin blood concentrations at presentation and 1 hour later, in combination with clinical assessment and an electrocardiogram.

Current US guidelines recommend troponin testing in patients with suspected MI at presentation and then 3 to 6 hours after symptom onset in low-risk patients. Although high-sensitivity assays have been available in Europe for at least 5 years, the first commercially available test—Roche’s Elecsys Troponin T STAT assay—only received 510(k) clearance from the US Food and Drug Administration (FDA) in January 2017. Since then, the FDA has cleared other high-sensitivity troponin I (hs-cTnI) assays, including one made by Siemens and another by Beckman Coulter Diagnostics.

Brent Muhlestein, MD (Intermountain Healthcare, Salt Lake City, UT), who was not involved in the study, said physicians are excited about the prospect of using high-sensitivity assays for patient triage and that while US centers have been slow to adopt their use compared with European hospitals, this is likely to change in the coming months and years with increasing availability.  

Referring to the experiences of physicians in the latest study, Muhlestein said the results reinforce the challenges needed to be addressed with the high-sensitivity assays. While the sensitivity and negative predictive value were perfect, the positive predictive value means there are a significant number people with abnormal test results who don’t have MI, he told TCTMD.

Regarding the positive predictive value, the researchers stress that “clinical judgement 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 other countries.”

One US Hospital’s Early Experience

At Parkland Health and Hospital System in Texas, the researchers tested the novel hs-cTnT protocol by comparing the number of patients who would have been eligible for early rule-out at 1 hour using the algorithm compared with conventional practice using cTnT testing at baseline and ≥ 3 hours after presentation. In 536 symptomatic patients presenting to the emergency department, cTnT and hs-cTnT were measured at 0, 1, and 3 hours after presentation. Individuals were classified into two categories—no MI (ruled out) or abnormal results—on the basis of troponin levels and changes over time.

Using the conventional cTnT assay, 80.4% were ruled out for MI by 3 hours. With the hs-cTnT algorithm, 83.8% of patients were ruled out for MI by 3 hours, including 30.0% at baseline, 24.8% at 1 hour, and 28.9% at 3 hours. With the conventional cTnT measurement, 19.6% had an abnormal test result compared with 16.2% using the hs-cTnT assay.

Unlike the ESC-recommended 0/1-hour algorithm, physicians modified their protocol to include the 3-hour hs-cTnT measurement for those considered “indeterminate” for MI following the test result at 1 hour. Using this modified algorithm, 87 patients overall had an abnormal hs-cTnT value and 449 were ruled out for MI. Using the ESC 0/1 algorithm, 85 patients were ruled in for MI and 297 patients were ruled out, but 154 patients were classified as needing further observation.

“A subtle but important distinction of our protocol from the ESC 0/1 protocol is the classification of individuals as ‘abnormal’ rather than ‘rule-in,’” write Vigen and colleagues. “We recommend a similar approach in other centers with an anticipated low MI prevalence among those undergoing troponin measurement.”

Switching to the high-sensitivity assay takes a multidisciplinary approach, but Das said that if a hospital or health system is able to make the necessary changes to their chest-pain processes of care, the modified treatment algorithm they used at their center is generalizable to other US hospitals. 

Muhlestein added that the 3-hour measurement—the modified algorithm—attempts to account for the fact that patients sometimes have normal but mildly elevated troponin levels, and that clinical judgement will be critical. “It looks very promising,” he told TCTMD. “Of course, troponin isn’t the only thing you use to diagnose acute coronary syndrome. You need to look at how sick they are, their TIMI risk score, and sometimes you don’t even need the troponin because you know it’s the real deal.” However, the high-sensitivity assay, based on the results of the present study, suggests that 55% of patients can be safely ruled out within an hour.

At their center, Muhlestein said physicians use cardiac troponin I assays for the diagnosis of MI—and they’ll likely incorporate hs-cTnI into their hospital system—because it’s less affected by renal dysfunction and other clinical factors, which they suspect will reduce the incidence of false-positive results.