The power of high-sensitivity troponin assays in the emergency department

Cardiac troponin is a critical biomarker for acute coronary syndromes (ACS). In part one of this two-part webinar series, Dr. Frank Peacock, emergency physician, professor of emergency medicine, and vice chair for research at Baylor College of Medicine, reviews the utilization of high-sensitivity troponin assays in the assessment of ACS, including the advantages of high-sensitivity troponin over contemporary assays and its impact on the management of patients presenting in the emergency department (ED).

Think you’d benefit from this webinar but missed it? You can now watch it on demand at any time that suits you and read on for highlights from the Q&A session.

You can also register free for part two: Time: The most precious resource, which will run Thursday, March 18, at 16:00 GMT/ 17:00 CET / 8:00 PST / 11:00 EDT.

Attendees to both events are entitled to P.A.C.E. credits from the ASCLS and/or ACCENT credits from the AACC.

Q: What is important for clinicians to consider when switching to high-sensitivity troponin, to avoid any confusion?

FP: There are two schools of thought on making the switch. The first is to just rip off the band-aid someday and change everything. I'm a little concerned by this method because it allows the opportunity for error, but you're done in two weeks. The second way is to change it slowly, having a period where you run both contemporary and high-sensitivity results. The advantage of this is in areas where high-sensitivity troponin or any troponin testing doesn’t occur very often, it allows a smoother transition, whereas in places with lots of high-sensitivity troponins, such as the emergency room and the cardiology department, the transition will occur very quickly. This is a decision that is made by the institution. There is no data that either one of those methods is superior to the other; the key is that both of them require a tremendous amount of education. You can really mess up when you switch from contemporary to high-sensitivity, and this is often due to the cut point. So there has to be extensive education on the cut point, and it has to be for your specific assay because every troponin I assay has a different cut point series.

Q: Some cardiologists are concerned that this will increase the number of unnecessary consultations, what are your thoughts on this?

FP: This again comes down to education. When troponin was only an MI marker, we consulted cardiology for every elevated troponin. Now that it is not just an MI marker, you need to use your brain. Cardiologists don't need to be in the loop for every single elevated troponin, that is clear. There will be an education period and probably some of them will get consulted and become a part of that education, but this would only last for a few months. The change is coming, we have just got to figure out how to do it smoothly.

Q: Is it more important to use sex-specific cut-offs when using high-sensitivity troponin?

FP: Yes. If you are using troponin I, you should use sex-specific cut points. There's no reason not to. You can get the lab to report the cut points on the sheet – it's a no-brainer. This is not the case for troponin T, as it is less sensitive to sex deviations than troponin I. So, I think for troponin I, you should use sex-dependent cut points, but not for troponin T.

Q: Do you recommend using a risk score in conjunction with high-sensitivity troponin?

FP: There are times when it's helpful and times when it's not. When a patient’s troponin is really, really low, below the fiftieth percentile, you don’t need a risk score because it's not going to add anything. That patient could be discharged. When it's really, really high, well above the ninety-ninth percentile, that person is not going home and again a risk score is not going help. This is because a risk score is not a diagnostic score tool, it's to decide whether someone can be managed as an outpatient. The population of people for which a risk score is helpful consists of those who are below the ninety-ninth percentile and above the cut point of low risk, fiftieth percentile, or the LoQ. For those patients, you do a pair of troponins and if they are unmoved you can then decide whether they need a stress test or if they can go home. This is where I find that the risk scores are helpful. The most commonly used risk scores are HEART and EDACS, and both are easy. Both provide superior safe discharge rates compared to physician judgment alone or from the older scores like TIMI. I do think as we move to better and better troponins, at some point risk scores will not be helpful, but currently, they are still useful for the middle-risk zone.

Q: With implementation of the 6 ng/L cut-off, most patients get a second test and have to wait for three hours. Do you have any suggestions to increase the cut-off?

FP: There is a number at which you can say they are so low, that one test is acceptable, and this will be different for every single troponin assay. The key is the hours since symptom onset. If you've had symptoms consistently for three hours, and I didn't test you when they started, but three hours later I do a test, this is like a zero and three, even though I don't know that first result. If that three-hour troponin is low, then I'm done. You can do that, but you have to know the history of the patient you're talking to.

I have currently got unpublished data from where we tested 49 patients under an hour, and low troponins were still extremely predictive of good outcomes. However, I would like all my patients to have at least three hours of symptoms – that's what the guidelines say. Very low troponins mean that you are very unlikely to have an adverse event, if it's anything that's not very low, then you have to do two troponins to make sure that it's not moving. Nothing makes troponin move like an MI – it goes up really quickly. If you take them a couple of hours apart and there is no movement, then it’s probably fine. But if there is movement, then you have to be concerned. For this, the ESC guidelines have some of the best numerical definitions available for deciding if a movement is large enough to be worried about.

Q: What about age-specific cut-offs?

FP: We know that the older you get, the higher your troponin is – this is just a natural thing. The challenge is knowing what a healthy normal cut point is for an older patient. Currently, I use the population-derived cut points and I understand the older people will frequently be on the edge of getting close to ‘you are ill’. You will see that older people are also the ones that are put into observed groups and kept because every risk score will put the elderly at tremendously high risk. If you're 85, you're probably going to stay in the hospital for 24 hours while we sort it out – that's what the risk scores will do. There are very few 85 year olds with a troponin below the LoD. Obviously, it's the population we don’t want to hospitalize, but it’s also the population with the greatest risk, and we don’t want them to be sent home inappropriately. This is a challenge and it's going to take some big studies to comfortably say what the upper reference level is for the elderly.

Q: How much faith is put into the actual definition of high-sensitivity troponin 1. Many tests seem to be marketed as high-sensitivity troponin 1 but not meet the definition, say with sex-specific cut-offs or measuring 50% female normal above an assay LoD. How important are these facts?

FP: They are important. A troponin assay is defined as being high sensitivity or not based on the number of normal people who have detectable levels. If you have a fifth-generation high-sensitivity troponin, everybody should get a number. If you have a third- or second-generation, you will draw troponins on a bunch of people, and some will come back undetectable. For these, it's not that it was undetectable, the assay just couldn't get that low. So now, in order to name a troponin assay as high sensitivity, there has to be a detectable number from the result in at least 50% of everybody tested. It is true that some assays have not done that, and they want to market themselves as high sensitivity. As consumers, we need to hold their feet to the fire and say that you can't call it high sensitivity unless it meets this threshold. At least half of everybody tested, male, female, Asian, African American, whatever, every subgroup has to have at least 50% detectable numbers, otherwise, we're not going to call it high sensitivity.

Q: Besides the lab and ED, who else should be included in the discussions when switching to high-sensitivity troponin?

FP: Cardiology. The big three users are gonna be the lab, ED, and cardiology. However, I will also say that the hospitalists need to be in the conversation too because when I get a troponin that is slightly elevated and it's due to a patient’s pneumonia, I'm going to send them to the intensive care unit, and the hospitalist or the intensive care doctor is going to have to take care of that. They need to be on the education panel too. It is probably one of those scenarios where you have some groups that get intensive specific training and other groups that get an email describing the changes and the algorithm the hospital intends to use. Emergency doctors and the cardiologists should sit down together and figure out where are they going to call the cut points, ‘when are we going to say this is so high it's probably an MI?’ and ‘where is the type 2 probability group and where do they go?’ An algorithm will need to be developed and should be available to everybody who is caring for patients and might draw a troponin.

Register for part two of this webinar series to explore the impact of delayed care in the ED setting and the value of point of care >>

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