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June 28, 2020
Rapid results alone not enough to justify devices’ use in emergency settings; higher analytical sensitivity needed to rule out hospitalizations.
Simply returning rapid results is not sufficient for implementing point-of-care testing (POCT) for cardiac biomarkers. A review article stresses the need for clinical labs, cardiologists, and emergency departments to collaborate on proper decision-making protocols to deliver cardiac biomarker results in a timely manner. “If you don’t do that, you don’t improve patient flow, and you won’t get the benefit of point-of-care and, more importantly, the benefit of high sensitivity troponin measurements,” the review’s author, Paul Collinson, MD, a professor and honorary consultant cardiologist at St George’s University Hospitals NHS Foundation Trust in London, told CLN Stat.
Collinson’s article reviews the current state of POCT for cardiac biomarkers, including strengths and limitations, comparison to central laboratory testing, and its role in the rapidly developing field of high sensitivity troponin (hs-cTn) assays. POCT proficiently measures cardiac troponin T (cTnT) and cardiac troponin I (cTnI). However, the introduction of hs-cTn assays and rapid rule-out algorithms for categorizing and discharging patients within 1 to 2 hours has complicated matters for POCT methods.
Until recently, POCT devices have enjoyed diagnostic equivalence to conventional lab assays in some circumstances. However, POCT assays simply aren’t as sensitive as the new hs-cTn assays on the market, which means “they can’t be used in the rapid decision-making algorithms that have been developed and well validated around the world,” Collinson said. Specifically, POCT assays lack the ability to detect low levels of troponin with the same degree of sensitivity as central lab tests. They also can’t measure repeat values at the low levels achieved in labs. “That’s the real difference at the moment,” he added.
Hospitals are relying increasingly on rapid results for measuring cardiac biomarkers. Several groups, including the U.K. National Institute for Health and Care Excellence, to which Collinson is a contributing expert, and the European Society of Cardiology have issued similar decision-making protocols for rapidly measuring cardiac troponin. Under this strategy, patients presenting with chest pain at a hospital receive a single hs-cTn test on admission, in addition to an electrocardiogram and clinical assessment. A decision to discharge can be made on this alone.
“If you use a hs-cTn assay, you can decide to discharge or repeat the measurement 1 to 2 hours later. Based on the initial value, and the change between the two values, you can categorize the patient as being able to go home safely or admitting them for more evaluation,” Collinson explained. The paradigm shift with hs-cTn assays is, even in the worst-case scenario, “after 3 hours, the patient is done and dusted. The hospital has all the information it needs.”
POCT assays are useful in reading high values of troponin, thus signaling a need to admit the patient to the hospital. “However, you can’t use a POC assay to rule out admission or to rule out after 1 to 2 hours. You have to wait to test at 3, possibly at 6 hours,” to get an affirmative result, according to Collinson.
While preliminary evidence suggests that POCT is catching up to central laboratory methods, it still lacks proper documentation and validation. Several POCT cardiac marker assays are now on the market, including Mitsubishi’s PATHFAST assay, which has been approved by the Food and Drug Administration. The problem with these assays is no one has validated them using whole blood in real time in clinical practice.
Developers of POCT cardiac biomarker assays will have to raise their game and provide assays as good as central lab testing, Collinson emphasized. “They must demonstrate high sensitivity analytic performance, and secondly, they must show that when you use one of these things in real world, it actually does what it says it does.”
Providing that POCT developers deliver a reliable assay that works in clinical practice, laboratory-based troponin measurements likely will eventually shrink away, Collinson predicted. “If you can do a test with a 15-minute turnaround time in front of the clinician, this will make them act quickly on their results—and that will result in changes in patient management.”
For now, however, “the [POCT] methods aren’t quite good enough,” concluded Collinson.