Troponin assays speed diagnosis, studies show
WEDNESDAY, Aug. 26 (HealthDay News) -- Two new European reports should help doctors decide which tests they choose to use for diagnosing possible heart attacks in emergency room patients, cardiologists say.
Both studies, which appear in the Aug. 27 issue of the New England Journal of Medicine, looked at tests for troponin, a protein released by damaged heart cells. Standard practice in most hospitals now calls for a troponin test when a heart attack or other major coronary problem is suspected, with a variety of tests commercially available for two forms of the protein, designated troponin I and troponin T.
One of the studies, done primarily in Switzerland, compares the accuracy of four new tests with that of a widely used older assay. The other, led by German physicians, compares tests done for the I and T forms of troponin.
"Both of these studies show that newer assays that are becoming available have a much better sensitivity, detecting even smaller amounts of damage," said Dr. E. Magnus Ohman, director of the program for advanced coronary disease at Duke University. Ohman, an expert on coronary diagnosis, was not involved with either study.
But because of the newness of the tests, "most physicians are uncertain about how they should be used," Ohman explained. The new tests will be a matter of intensive discussion by representatives of the American Heart Association, the American College of Cardiology and the European Society of Cardiology at a meeting in Barcelona next week, he added.
The German study compared newer tests of the two forms of the protein with older tests now widely used in suspected heart attacks. The study of 1,818 cases found that the newer troponin I test was more sensitive in detecting heart damage and more specific in determining that the damage was due to a heart attack, a group led by Dr. Stefan Blankenberg of the University Medical Center Mainz reported.
The troponin I test was better than 90 percent sensitive in detecting heart damage and 90 percent specific in determining whether it was due to a heart attack, the study found.
A second study led by Swiss cardiologists reported on the use of newer tests for both troponin I and troponin T on 718 people who came to emergency rooms with symptoms indicating possible heart attacks.
"The diagnostic performance of sensitive cardiac troponin assays is excellent, and these assays can substantially improve the early diagnosis of acute myocardial infarction [heart attack], particularly in patients with a recent onset of chest pain," the researchers wrote.
The choice of a troponin test still might not be easy, Ohman said. For example, he prefers a test for troponin T. That is a minority choice in the United States, where about 60 percent of physicians test for troponin I, Ohman said.
More studies probably are needed to help doctors make a choice, he said. "We need to assay the sensitivity of tests in a broader range of patients," he said of the European studies. "I suspect that they had many more patients and somehow selected out the more likely cardiac patients. We need to do many more studies on patients with a lower chance of cardiac disease."
The increased sensitivity of the newer tests might pose a problem in some cases, Ohman said. "Once you are able to detect smaller and smaller infarcts [damaged heart areas], you can be detecting damage that may not be a clinical heart attack," he said, which would complicate the choice of treatment.
Increased troponin levels can be due to "a whole host of conditions" other than a heart attack, including inflammation from myocarditis and even strain on the heart from blood clots in the lung, Ohman said.
The increased sensitivity of the newer tests might raise some issues, but the two studies "should provide an increased level of confidence for clinicians that we are moving in the right direction," said Dr. David A. Morrow, an associate professor of medicine at Harvard Medical School and director of the Levine Cardiac Unit at Brigham and Women's Hospital, who wrote an accompanying editorial.
The tests described in the studies "do perform better than other tests. They are more sensitive and there are fewer missed heart attacks in the emergency room," Morrow said.
His unit already has adopted one of the newer tests, which assays levels of troponin I, he said. But a physician can do well with any of the new tests, Morrow said. "Knowing the assay and how it performs is more important than whether it assays for I or T," he noted.
Blood tests used to diagnose heart attacks are described by the American Heart Association.
SOURCES: E. Magnus Ohman, M.D., professor, medicine, and director, program for advanced coronary disease, Duke University, Durham, N.C.; David A. Morrow, M.D., associate professor, medicine, Harvard Medical School, and director, Levine Cardiac Unit, Brigham and Women's Hospital, Boston; Aug. 27, 2009, New England Journal of Medicine
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