Is the effort really worth the result: hs-cTn at the point of care or lab

The value of high-sensitivity troponin in the assessment of patients with suspected acute coronary syndrome (ACS) has been well established in clinical practice guidelines.

In this on-demand SelectScience^® webinar, Dr. Frank Peacock, Baylor College of Medicine moderates a debate between Dr. Louise Cullen, Royal Brisbane and Women's Hospital and Dr. Rick Body, University of Manchester. The debate centers around the best placement for high-sensitivity troponin assays, whether at the point of care in the Emergency Department (ED), or from the central laboratory. These esteemed emergency physicians elucidate the potential advantages of each setting regarding the integration of high-sensitivity troponin results as an aid in the diagnosis of Acute Myocardial Infarction (AMI) and the potential for improvement of patient disposition decision timelines.

Read on for highlights from the live Q&A or register to watch the webinar at a time that suits your schedule.

There's a concern that a high-sensitivity troponin assay will lead to troponinitis, with many patients potentially receiving unnecessary investigations and treatment. Will point-of-care high-sensitivity troponin make the situation worse?

RB: Troponinitis is not a popular term because it suggests that we trivialize the problem of elevated troponin. If you see a troponin that's elevated, it's elevated for a reason. Whatever that reason is, it means something bad has happened with your heart, whether it's chronic or acute. What we want to avoid is over-investigation of patients and reacting to chronic or acute myocardial injury that's just there because a patient is sick and maybe we are over-investigating and overtreating. I think the point-of-care troponin testing will help us to address this issue.

One of the problems is a long turnaround time for the lab tests at the front door of the emergency department and we want the information to be ready as soon as possible. Those taking blood in the UK in the emergency department will tend to be cautious. When you've got a point-of-care assay with a turnaround time of 20 minutes or less, you don't need to worry about that quite as much. You can perhaps wait until the doctors reviewed the patient and only do the test if they suspect an acute coronary syndrome. Therefore, I see point-of-care troponin testing as helping to avoid over-investigation in these patients.

LC: One of the things that Rick has just highlighted is the differences in systems. Rick’s talking about how in the UK, people take blood well in advance. We're not there yet within the Australian context, which means that we actively have a say in what blood tests need to go off. Our chest pain patients will come as a CAT1, you'll take a brief history, get their ECG within 10 minutes, and at that point in time, you're also directing the staff as to what tests to be taken. Therefore, their utility will differ in different systems and I think that is one of the opportunities for tailoring of point-of-care troponin moving forward.

Is there any value to risk scores in a patient whose troponin is below the high sensory point in assay level of detection?

RB: The limited detection cutoff has been well validated. We know that we can be very confident that patients with a troponin below the limits of detection (LOD) don't have an AMI. However, there are two important caveats to that. One is that a lot of the studies only look to that strategy in patients with a normal ECG in the absence of ECG ischemia, so don't ignore the ECG.

The second point that is important to bear in mind is time from symptom onset. The limited detection strategy for some assays has been well validated for patients who've got a symptom onset above a certain threshold, say three hours. But in very early presenters, not quite so much. In fact, for some assays, there's evidence that the sensitivity goes down in those early presenters.

In general, if you've got a patient with a troponin below the LOD, you've got a normal ECG, had there been a reasonable time from symptom onset, you probably don't need to consider other information to rule out an AMI But the risk scores can help you because they can identify other patients so you can discharge on top of that, and they can risk-stratify the remainder so they can help you send patients to the appropriate area of the hospital and help you to rule it in.

FP: So, the magic number for you Rick, is three hours of symptoms. Louise, do you agree? Can a patient be ruled out if they've got a low troponin and had at least three hours of symptoms?

LC: Probably less than that and I think we need to debunk that. I think that Rick's very right, the papers that you look around now will talk about three hours since symptom onset. The reality, though, is that often it's because the proportions of patients that actually meet that criteria are very small in all of the studies. Our median time from onset of symptoms to arrival is about four hours locally. People sit at home, thinking about it before they call the ambulance services to get transported. It’s going to take a big international collaborative study to debunk it. My gut feeling is that we're probably not right. It's not the troponin alone, it's never the troponin alone, it's the context as well which is important.

FP: Yes, I think that's absolutely an important point in the context. We are not looking at numbers and ignoring the patient, you must take it all in.

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