New Blood Test May Quickly Rule Out Acute MI

Novel Point-of-Care Troponin Assay May Facilitate Faster Rule-Out of AMI




A new point-of-care troponin assay can safely rule out acute myocardial infarction (AMI) in just 15 minutes in a large proportion of patients with symptoms suggestive of acute coronary syndrome, according to a preliminary study.

"This is a big change because now it's possible to safely rule out myocardial infarction in almost 60% of patients with a single blood test that only takes 15 minutes to run," Martin P. Than, MBBS, from Christchurch Hospital, New Zealand, told theheart.org | Medscape Cardiology.

Than and colleagues found no difference in discrimination between the new Abbott i-Stat TnI-Nx Point-of-Care Assay and a high-sensitivity troponin I (hs-cTnI) comparator assay in ruling out AMI, as measured by the area under the curve (0.975 vs 0.97; P = .46).

A TnI-Nx assay result of less than 11 ng/L identified 56.7% of patients as low risk. The sensitivity was 100%, and the negative predictive value (NPV) was 100%.


For the hs-cTnI laboratory-based assay (Architect, Abbott Diagnostics), a result of less than 3 ng/L identified 43.5% of patients as low risk, also with sensitivity and NPV of 100%.

Their results were published online October 17 in JAMA Cardiology.

In this preliminary study, the New Zealand group assessed plasma samples from 354 adults who presented with symptoms suggestive of AMI to a single urban regional emergency department (ED) in Christchurch. The blood was drawn a median of 4.5 hours after symptom onset.

The new i-Stat TnI-Nx Point-of-Care assay is an enzyme-linked immunosorbent assay that improves detection of troponin I by leveraging paramagnetic beads and electrochemical detection of the resulting enzyme signal. It cannot yet be designated as being a high-sensitivity test because such a designation requires extensive population-based testing, which has not yet been completed.

Abbott's handheld i-Stat platform is already being used for other point-of-care applications. This newest test, which is not yet commercially available, combines higher sensitivity with several enhancements to speed up testing.

"If shown safe and effective, anything you can get back in 15 minutes is a huge advance," said L. Kristin Newby, MD, MHS, Duke University School of Medicine, Durham, North Carolina, in comments to theheart.org | Medscape Cardiology.

This trial comes on the heels of the High-STEACS trial, presented at the recent European Society of Cardiology Congress 2018, which showed a lack of improvement in 1-year outcomes with a high-sensitivity troponin assay. Both Than and Newby suggested, however, that those findings don't diminish these new results.

"I would not be discouraged by High-STEACS," said Newby. She noted that there were methodologic problems in the trial and that, in any case, "High-STEACS was looking at kind of the other end of the spectrum in terms of high sensitivity assays in terms of what do we do with people who have values above the 99th percentile, whereas this trial was more about rule out than rule in."

She is further reassured by recent studies that have shown a reduction in the use of stress testing with high-sensitivity assays, "particularly when used algorithmically," and that there was no increase in the use of coronary angiography or percutaneous coronary intervention.


Streamlined Triage in the ED

If brought to market, the Abbott Point-of-Care TnI-Nx assay could dramatically alter patient flow through the ED, as well as resource allocation, they say.

"If you're a rule in, it's good, because you get attended to faster, and if you're a rule out, it's terrific for flow through the emergency department," said Newby.

"It's not just the additional 45 minutes you're saving," added Than, referencing the roughly 60 minutes needed to get a result from a "standard" laboratory-based high-sensitivity troponin assay.

"When I go to see a chest pain patient, the troponin result isn't ready by the time I've finished my assessment, so I go off and do other things, and it could take hours to get me back to the patient and determining next steps.

"With a turnaround time of 15 minutes, the result will be available by the time the doctor finishes his initial assessment and has to make a decision," he said.

Downstream, this greater efficiency could reduce overcrowding, limit the number of patients handed off to the next shift, free rooms faster, and result in faster treatment and improved outcomes.

Than and colleagues further suggest the new assay might be used to prevent "long and unnecessary transfers to secondary hospitals" or even remote triage in ambulances.

"These other uses are certainly possible and could potentially expand the reach of the lab, perhaps letting people avoid the emergency department or allowing for remote triage and better targeted transport," said Newby.

"It's going to take additional research, of course, but these things become possible when you have something like this available," she added.

The investigators stressed that the findings reported are only preliminary. Than's team is continuing to recruit patients and expects to be able to report on a sample of 3000 patients in early 2019, "with greater certainty around the threshold suitable for baseline rule-out discharge and the confidence intervals around it," he said.

They are also planning a much larger, 30,000-patient-strong study that will assess the impact of this assay on patient care and outcomes, as well as costs and ED flow.

The TnI-Nx assay can be used with either plasma or whole blood, in contrast to other assays on the market, which all require plasma. In this study, frozen plasma samples were used because of logistic considerations, reported Than, but his group intends to conduct a direct comparison of the assay's performance using whole blood and fresh spun plasma.

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