New Point-of-Care Troponin Assay Shows Promise for Ruling Out MI

A novel point-of-care troponin assay with improved precision compared with other similar tests may be useful for ruling out acute MI in the emergency department (ED) based on a single blood draw, with a turnaround time of about 15 minutes, a preliminary study shows.

The assay (i-STAT TnI-Nx; Abbott Point of Care)—which has not yet been designated “high-sensitivity”—ruled out MI with 100% sensitivity and a negative predictive value of 100%, according to co-lead authors John Pickering, PhD, and Joanna Young, PhD (Christchurch Hospital, New Zealand), and colleagues.

That performance compared favorably with that of a laboratory-based high-sensitivity troponin I assay (Architect hs-cTnI; Abbott Diagnostics), which also ruled out MI with a sensitivity and negative predictive value of 100%, the investigators describe in a brief report published online October 17, 2018, ahead of print in JAMA Cardiology.

The point-of-care assay “matched, if not bettered, the performance of a commercial high-sensitivity troponin I assay to safely rule out myocardial infarction,” Pickering told TCTMD in an email. He pointed out that the main advantage of the new test is that it takes only 15 minutes to get results.

“This is quick enough that the results would be available by the time the physician has finished examining a patient,” he said. “Typically, it takes 45 to 90 minutes to send a blood sample to a lab, have it registered, troponin measured, and the results returned to the emergency department. By this time the physician is likely to be busy with another patient, so may not see and be able to act on the results straight away.”

Andrew Chapman, MD, PhD (University of Edinburgh, Scotland), who was not involved in the study, said the delay while waiting for test results is one of the key challenges inherent to current approaches for rapidly ruling out MI.

“A bedside cardiac troponin test which is able to match the diagnostic performance of a laboratory system would potentially reduce sample turnaround time and increase the time available for staff to assess patients and seek alternative diagnoses,” he told TCTMD in an email.

Chapman indicated, however, that the utility of this particular assay requires additional study. “If this can be successfully validated in a prospective trial, this assay may give clinicians the opportunity to confirm or refute the diagnosis of myocardial infarction at an earlier stage,” he said. “At present, the findings in isolation are cause for optimism and further research.”

Ruling Out MI With a Single Troponin Test

Prior research—including a meta-analysis and a systematic review—have shown that high-sensitivity troponin assays are accurate enough to rule out MI in many patients based on a single test at presentation. But those lab-based tests take time.

Point-of-care troponin assays that yield results within about 15 minutes have been introduced to help address the long turnaround time, but they lack precision at the lower concentrations detected by high-sensitivity assays, according to the authors. Thus, if the precision of these point-of-care assays can be improved, the time it takes to rule out MI could be shortened, allowing for early discharge in many patients.

The i-STAT TnI-Nx evaluated here is a new-generation point-of-care assay with greater precision. Pickering, Young, and colleagues evaluated its performance for ruling out MI based on a single blood test among 354 patients (mean age 62 years; 72% men) who presented to a single urban regional emergency department in New Zealand with symptoms suggestive of acute MI; 16.1% ultimately received a diagnosis of type 1 MI (primary outcome). 

The first blood sample was taken a median of 4.5 hours after symptom onset. Based on a single test using that sample, the discrimination ability of the novel assay for ruling out MI was similar to that with the high-sensitivity assay (area under the receiver operating characteristic curve 0.975 vs 0.970; P = 0.46).

The lowest concentrations of troponin measured with the point-of-care assay and the lab-based assay in patients diagnosed with acute MI were 11 ng/L and 3 ng/L, respectively. The proportions of patients below those thresholds—who were considered low risk—were 56.7% and 43.5%.

Not Yet Ready for the Clinic

The authors stress that these findings should be considered preliminary.

“While the performance to date is good, it should be noted that this study tested plasma rather than whole blood and that we did not directly compare the turnaround time of this assay within the ED with that of the central laboratory assay,” they note. “Additional studies are needed to assess whole-blood and bedside performance, cost-effectiveness, performance as a function of time from symptom onset, and performance in conjunction with clinical risk scores and electrocardiogram as well as create validated decision-making thresholds.”

Regarding the pricing of the new test, an Abbott spokesperson told TCTMD in an email that “because the product is still under development, we are not able to comment on cost.”

The next step, which is currently ongoing, is to perform a larger study to characterize the novel assay, Pickering said. “Following this, we plan a monitored implementation of this single test in our accelerated diagnostic pathway at multiple hospitals around New Zealand,” he said. “We will evaluate if the test reduces length of stay as is hoped. Application in the ED may, therefore, result in patients being reassured earlier that they are not having a heart attack. Additionally, there is likely to be a reduction in ED overcrowding.”

The investigators also plan on evaluating use of the point-of-care assay in rural hospitals and general practices that are not close to a central laboratory to see whether that may allow some patients who would otherwise be transferred to an urban center to be managed locally.

Chapman said there are some remaining questions about the assay, noting that the current report does not contain information on key diagnostic metrics like limit of detection and coefficient of variation at the 99th percentile, “which prevents comparisons of analytical assay performance.”

In addition, “it remains to be established if this assay meets criteria for high-sensitivity, and to determine the lowest concentrations which can be reported in practice,” Chapman said. “It is important to note that the samples were analyzed by the assay manufacturer, and prospective implementation studies measuring fresh blood samples at the bedside are required to demonstrate clinical staff can reproduce this performance in clinical practice.”

That said, if the new point-of-care assay is eventually adopted in practice, it could have important implications, Chapman suggested.

“If implementation proves successful, clinicians would be able to act on cardiac troponin results in as little as 15 minutes,” he explained. “This could mean earlier treatment in confirmed myocardial infarction, or alternatively, earlier screening for alternative diagnoses where this is ruled out. This could streamline decision-making for hospital admission and discharge, and in certain circumstances, such as in patients where there is a high suspicion of myocardial infarction, this could be helpful to redirect paramedics to hospitals where cardiac facilities are available.”