This news release describes the results of a study designed to significantly advance the search for a rapid blood test that can rule out evidence of heart muscle damage in people who come to emergency rooms with chest pain and other symptoms of heart attack. The study, reported in the journal The Lancet, specifically offers compelling evidence that a version of a commonly used blood test may indeed further that quest.
For the study, investigators used a highly sensitive version of an existing blood test that detects the protein troponin on more than 6,300 consecutive people presenting to hospital emergency rooms (mostly in Scotland) with suspected acute coronary syndrome. The researchers were able to determine the probability that patients were NOT at risk of heart attack or death from heart attack after 30 days for a range of troponin levels.
The release does a generally adequate job of describing how the high-sensitivity test appears to identify very low levels of troponin, in contrast to current troponin tests, thus making it theoretically possible to accurately, relatively quickly, and safely rule out a heart attack in more than 60 percent of such people, at least over the short term. It covers the fact that conventional troponin testing detects only higher levels of the protein, and must be done on serial blood samples over a longer period of time. And the news release puts appropriate emphasis on the potential the new test has for decreasing unnecessary hospitalizations and reducing health care costs.
All that said, the release could have done a much better job of making clear earlier in the text that substantially more research will be needed to determine the clinical effectiveness and safety of relying heavily on high-sensitivity troponin testing. Although the release uses qualifiers such as “may have been eligible for early safe discharge,” we think more needed to be said about potential risks, about the potential costs of the more sensitive test; and most of all about the limitations of the study and over-reliance on any single test when people experience heart attack symptoms.
Patients arriving at emergency facilities with chest pain is a common and costly situation that is associated with potentially devastating consequences when the evaluation isn’t done in a thorough fashion. The current evaluation of chest pain involves a history focused on the patient’s reported symptoms and past history of heart disease and risk factors as well as tests performed. These include an electrical test of the heart (EKG or electrocardiogram) and blood tests looking for damage to heart muscle. This evaluation has been standard for decades, but better blood tests over time have allowed emergency providers to more accurately and quickly identify patients who may be having a heart attack. At the same time, the use of these newer tests has permitted providers to more quickly identify those who are not having a heart attack, allowing for earlier discharge from the emergency facility or hospital. The study reported in this news release seeks to define the threshold below which a new, more sensitive test identifies people who are at low risk for heart attack or heart related death over the next 30 days. If confirmed, this will be a positive step forward in effectively and efficiently evaluating patients with chest pain in emergency facilities. However, the main limitation of this study is that it is using information previously collected to predict what would have happened if this new test and threshold was used. Only with prospective use and evaluation can we actually determine if this new test and threshold, when applied as part of routine care, leads to improved care and more efficient use of emergency and hospital resources.
The release makes repeated reference to claims by the study’s authors of substantial savings to the health care system, but no quantitative data are included. More significantly, there is no information presented about the cost of the high-sensitivity test or comparison to current per-patient cost for evaluating acute coronary syndrome in the British health care system. At a minimum, one would want to know the cost of this new test compared to standard troponin tests. Further work would be needed to assess the relative downstream costs associated with this new test.
This is a mixed bag. On the one hand, the news release refers to the high negative predictive value of the test (99.6%), which suggests that the test is very good at finding those who aren’t at risk of a heart attack or death over the next 30 days. But it also relies on relative risk comparisons, and does not offer data in absolute terms about risks of heart attack or cardiac death in those with various ranges of troponin levels. It refers to patients “at very low risk” of a heart attack in the next 30 days, but never tells readers what that means (1%? 5%? 15% chance of a heart attack?). Despite these shortcomings, we think the reader will come away with a decent understanding of the potential benefits of the more sensitive test, and so we’ll award a Satisfactory rating here.
The potential harms of this test — discharging a patient who may be having a heart attack and be at risk of dying — can only be adequately assessed in prospective evaluations using this new test as part of routine care. The release doesn’t adequately address this or describe what might happen if the test is wrong. We also think that the release could have done a better job of explaining that this new test is only one part of the assessment of patients presenting with chest pain. Other factors that are likely to be important that could have been mentioned from the paper include changes in the EKG (electrical test of the heart) that is also part of standard care. In addition, the duration of symptoms is also important. For patients who have had pain for less than 2 hours, the test may not be as effective.
The release would have been stronger had it offered more information about the design of the study and its limitations. We’d emphasize, as noted above, that the main limitation of this study is that it is using information previously collected to predict what would have happened if this new test and threshold were used. Only with prospective use and evaluation can we actually determine if this new test and threshold, when applied as part of routine care, leads to improved care and more efficient use of emergency and hospital resources. We acknowledge that the release hints at this limitation when it quotes from an accompanying editorial — “The ultimate validation for the safety and efficacy of discharging patients with cardiac troponin concentrations less than 5 ng/L will be the report of clinical outcomes after this threshold is implemented in routine clinical practice…” — but we think the release should have been more explicit about this aspect of the study, as the researchers were in the study itself. In the paper they caution much more directly, “Although we determined the number of patients who could be safely discharged, whether clinicians can effectively implement this threshold in clinical practice and whether this will substantially improve rates of discharge, is unknown.”
Anyone who has dialed 911 (or its British equivalent, 999) or worried at home about the meaning of chest pain will understand the need for a rapid, reliable way to rule out an emergent heart attack. No disease mongering here; the accurate diagnosis of heart attack is a serious issue.
The release duly notes funders.
The release does a pretty good job of comparing current troponin tests with more sensitive one used for the current study.
The release never explicitly states whether this is now being used, either at the study sites involved or elsewhere.
The news hook for this release is pretty well established.
Readers might interpret one of the quotes in this release as suggesting that the study is absolutely conclusive in terms of safety and efficacy. “These patients are therefore potentially suitable for immediate and safe discharge from the emergency department. These findings could dramatically reduce unnecessary hospital admissions and provide substantial cost savings for healthcare providers.” But since the language used elsewhere is more measured, we’ll let this one go with a warning.