Are Troponins Ready for Prime Time?

In the world of cardiology, wisdom holds that “seconds are cells, and minutes are muscle,” and that one of the best methods for improving patient outcomes is to improve efficiency and shorten the duration of patients’ cardiac events. 

At a physiological level, troponins are a class of protein found in muscle cells that help with muscle contraction. There are cardiac-specific troponins that come from heart muscle cells (myocytes). During active cardiac damage these cardiac-specific troponins can leak into the bloodstream.

Tracking cardiac troponin in blood samples has been well-established as the preferred biomarker to measure cardiac damage and is often used in hospitals as a means of identifying whether chest pain is of cardiac origin. National and international cardiology societies—including the American Heart Association, American College of Cardiology, and European Society of Cardiology—all emphasize the importance of troponin testing in informing clinical decisions. However, among prehospital providers there has been little adoption of checking the troponin levels of patients.

This is most likely due to the fact that troponin testing historically required sending blood samples to a lab for analysis, which limited it to hospitals and clinics with these capabilities. In recent years, however, many companies have launched point-of-care (POC) troponin testing solutions, which gives healthcare professionals the ability to get reliable troponin results directly at the bedside. The advent of these POC tests might mean that ambulance crews, for the first time, can conduct prehospital troponin tests and get the results in minutes. Furthermore, several influential studies have shown troponin testing might have a promising role in prehospital care.

High Predictive Value

Perhaps the most impactful of these studies comes out of Denmark. Published in the European Heart Journal, Aarhus University’s Martin Rasmussen and colleagues looked at data from 68 ambulances and 10 physician-led prehospital care teams given point-of-care troponin testing capabilities.

From June 2012 through November 2015, those teams conducted 18,712 troponin tests on 15,781 individuals. Based on their results, the investigators concluded that “routine troponin measurement in the prehospital setting has a high predictive value and can be used to identify high-risk patients even before hospital arrival with the possibility to reroute them directly for advanced care in a heart center.”¹  
This study showed troponin testing could be feasibly implemented in a large EMS system. Furthermore it showed that, given the large number of tests conducted during the period surveyed, EMS crews with the capabilities were willing to use the test in the prehospital environment.

There have been concerns as to whether prehospital troponin studies are of equal quality to those conducted in-hospital. Chicago cardiologist Joseph Venturini and colleagues sought to test this in a 2013 study.² They took blood samples from ER patients who complained of chest pain. They split the samples, with a part retained in the ED and a part placed in ambulances for simulated runs.

These runs were deliberately modeled after ambulance transports and had varying distances and routes. They conducted troponin tests at each site. When compared, there was virtually no difference in the results between the ED and moving ambulance tests, suggesting ambulance troponin tests can be just as reliable as those in hospitals.

In Manchester, U.K., the ongoing Prehospital Evaluation of Sensitive Troponin (PRESTO) study is looking at the implementation of prehospital troponin testing. Seven hundred study participants who call for an ambulance complaining of symptoms of a cardiac event will have blood drawn both in the ambulance and the receiving hospital. Later these samples will be analyzed for the presence of troponin.

Patients’ records will also be examined for outcomes and ultimate diagnosis and compared to the results from the two troponin tests. The study is set to conclude in the spring of 2020. Investigators hope to find instances in which prehospital troponin testing proved valuable as well as identify the best practices for EMS adoption of troponin testing.³ 

A Poor Negative Predictor

Studies have also found that while it can have good positive predictive value, prehospital troponin is a poor negative predictor for ruling out whether a patient is suffering from an adverse cardiac event. A 1998 study found that among 29 patients diagnosed with acute coronary ischemia, cardiac troponin T testing showed positive results in only five patients.⁴ Of these, three were found to be having AMIs, and two were experiencing unstable angina. The mechanisms used for troponin testing have advanced since this study’s publication, but it remains true that a negative troponin test cannot be used to definitively rule out the presence of an adverse cardiac event.

Prehospital troponin testing’s role might lie in helping make clinical decisions only when the test results are positive. Let’s say a crew has been called to a patient complaining of chest pain. They conduct their regular cardiac workup (ASA, 12-lead, nitroglycerin), and the 12-lead appears to show sinus rhythm. They transport the patient to the ER, where the attending physician orders a troponin test. In this scenario the patient has to wait for the hospital’s lab to process the sample and analyze the results, potentially adding to the time they might be suffering from an adverse cardiac event. 

Now say this same scenario happens to a crew with troponin-testing capabilities. The EMS crew can relay the news of a positive test during the transfer of care or by phone, and the patient can be expedited to advanced cardiac care, saving valuable time. It’s possible even a negative test will save time because the receiving facility need not perform a test of its own. Ultimately this will require broad acceptance that a prehospital troponin test is as reliable as an in-hospital test.

It might seem like the stars need to align for a troponin test to prove valuable. But considering how widely used the test is in hospital settings, adding this capability to prehospital care could prove worthwhile, especially given the advances in measurement devices. In the coming years it will be exciting to see more EMS agencies adopt troponin testing and learn from them how to effectively use the results to influence patient care. 

References

1. Rasmussen MB, Stengaard C, Soerensen JT, et al. Prehospital point-of-care troponin measurement predicts outcome and diagnosis in patients with suspected acute myocardial infarction—Experiences from a large routine-use cohort. Eur Heart J, 2017 Aug; 38(suppl 1).

2. Venturini JM, Stake CE, Cichon ME. Prehospital point-of-care testing for troponin: Are the results reliable? Prehosp Emerg Care, 2013; 17: 1, 88–91.

3. National Library of Medicine. The Pre-hospital Evaluation of Sensitive Troponin (PRESTO) Study. ClinicalTrials.gov, https://clinicaltrials.gov/ct2/show/NCT03561051.

4. Newman J, Aulick N, Cheng T, et al. Prehospital identification of acute coronary ischemia using a troponin t rapid assay. Prehosp Emerg Care, 1999 Apr–Jun; 3(2): 97–101.

Other Resources

Gardezi SA. Troponin: think before you request one. BMJ Qual Improv Rep, 2015 Mar 25; 4(1). 

Sharma S, Jackson PG, Makan J. Cardiac troponins. J Clin Pathol, 2004; 57(10): 1,025–6.

Wu AH, Apple FS, Gibler WB, et al. National Academy of Clinical Biochemistry Standards of laboratory practice: Recommendations for the use of cardiac markers in coronary artery diseases. Clin Chem, 1999; 45: 1,104–21. 

Aditya C. Shekhar is a research scientist, EMS educator, and writer. His articles about the physiologic progression of heart attacks have been read globally and won awards in the field of cardiology. He has taught paramedic, EMT, EMR, and CPR courses in the United States and internationally and has designed online educational content for EMS providers.