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August 6, 2019
Imagine that you present to an emergency department with left-sided chest pain and need to be worked up for possible myocardial infarction (MI). Would you want the lab to use the most sensitive assay available or use the less sensitive assay because it has been used for years? Embracing change with open arms isn’t always easy but this particular one—implementing high-sensitivity cardiac troponin (hs-cTn) assays—is here now, and it is our duty as laboratorians to get on board.
The use of increasingly sensitive cTn assays for excluding or diagnosing acute MI has become universal. With several hs-cTn assays already U.S. Food and Drug Administration (FDA)- approved and more on the way, many U.S. laboratories have already or are in the process of implementing the new assays. For those labs who are not embracing the move, now is the time for a unified approach to implementation.
At the Sunday AACC University session, “Clinical Laboratory Practice Recommendations for Use of High Sensitivity Cardiac Troponin Assays,” the speakers, all of whom have participated in hs-cTn assay research and also implemented these tests clinically, included Fred Apple, PhD, Brad Karon MD, PhD, Judd Hollander, MD, and Allan Jaffe, MD. They shared evidence-based background with the audience about why it’s smart to switch and practical tips about how to incorporate high sensitivity cTn independent of which assay (cTnT or cTnI) is being implemented. The session covered both clinical and analytical aspects.
From the analytical point of view, Apple discussed the recommendations in the IFCC guidelines with the important message being “to know your assay” as all assays are not the same. Karon discussed the laboratory experience in the use of the high sensitivity assays for the past year and one thing stood out: platform to platform variability exists, and calibrations can also lead to variability in the assays.
Organizations face two major challenges during implementation. The first involves a change in reporting units. Second, hs-cTn assays should have sex-specific rather than total 99th percentile figures. Overcoming these challenges boils down to proper education and communication between laboratorians and clinicians.
Speaking from the clinical point of view, Hollander, who is an Emergency Medicine Physician, spoke on the importance of clinicians working together with the laboratory in implementing the 5th generation troponin assay. He made it very clear to the audience that when it comes to the clinical use of troponins in the ER, “Any troponin is worse than no troponin and more troponin is worse than less troponin.” He also reminded the audience that troponin levels are an aid to diagnosis and do not mean MI is present as there may be increase due to other myocardial injury or non-cardiac causes.
To further re-iterate the clinical use of high sensitivity troponin assays, Jaffe in his presentation used real life cases to demonstrate that elevated troponins even with a delta of zero may need to be looked at more closely and may be a pointer to a more serious disease. This can happen especially in atypical patients like those with MI with non- obstructive coronary arteries (MINOCA).
Some providers have concerns that hs-cTn assays may yield higher false positive results, but the speakers emphasized this is not necessarily the case. This would be true, however, when comparing some insensitive 4th generation assays to the new hs-cTn assays. With the new assays, a positive result will be clinically meaningful since levels above the 99th percentile will not be due to analytical issues.
All the speakers agreed on the fact that an important aspect of interpretation is the use of the delta value rather than individual numbers.
Based on early data from the CONTRAST study, Apple advised strongly against substituting a cTn I assay with a cTn T assay. There’s not a perfect correlation between these assays, and if a lab switches from one to the other, a full method validation with significant communication to clinicians about the change will be necessary.
Using point of care (POC) assays in the emergency department may lead to an initial false negative result since these tests are not nearly as sensitive as lab-based hs-cTn assays. The speakers strongly advised labs to meet the turn-around time of <60min for hs-cTn assays and not switch between a POC assay and a lab-based test. At this time, the speakers stressed, using a POC cTn assay will not offer any benefits in settings where hospital labs perform hs-cTn testing.
Apple in his conclusion said, “Do not be afraid to move forward with the high sensitivity assays, it is the best in patient care for troponin assays.” Given this deep dive into hs-cTn assays, the speakers hope attendees will move forward expeditiously in implementing these new diagnostic tools.