New, extra sensitive tests for troponin
- a protein released by dying heart cells - may help diagnose heart attacks
well before conventional tests can, according to two recent studies.
Troponin tests, along with electrocardiograms that measure the heart's electrical activity, have for years been major tools for spotting heart attacks. Typically, any detectable level of troponin in the blood indicates some degree of heart damage. But levels of troponin that are high enough to be measured by conventional tests can take hours to accumulate, meaning that heart attack patients must wait in emergency rooms for that length of time before test results are available. The newer, more sensitive tests can detect troponin at lower levels and may be able to point to a heart attack much sooner after onset of symptoms.
Writing in the August 27 New England Journal of Medicine, reports by two research teams, one Swiss and one German, show that the new tests are able to measure troponin levels when patients with chest pain first arrive at hospitals. Performing sensitive troponin tests as soon as doctors suspect a heart attack might speed diagnosis, save lives, and save billions of dollars, authors note.
The Swiss researchers showed that new troponin tests sold by four companies were somewhat more accurate in diagnosing heart attacks than an older troponin test when used in patients shortly after their arrival at hospital emergency rooms. They tested blood samples from 718 patients with symptoms that suggested heart attack.
In persons who were seen within two hours of the start of their chest pain, the new test was able to diagnose heart attacks accurately 89% to 94% of the time, compared to 70% for the conventional test. Overall, the newer tests correctly identified troponin levels indicating heart attacks between 95% and 96% of the time, while the conventional test did so 90% of the time.
"The diagnostic performance of sensitive cardiac troponin assays [tests] is excellent, and these assays can substantially improve the early diagnosis of acute myocardial infarction, particularly in patients with a recent onset of chest pain," conclude the Swiss authors, who note that the companies that market the four tests helped pay for the research.
The second study, conducted at three German hospitals, found that among blood samples obtained soon after patients experiencing chest pain arrived at hospitals, the new troponin test was the most accurate in diagnosing heart attacks, compared with the conventional troponin test and other markers. The new troponin test identified 84% of patients with levels suggesting heart attack, while the conventional troponin test identified 55% such patients.
However, the German researchers cautioned that more studies should show that quick diagnosis of heart attack actually improves results for patients before the new, sensitive tests are used more widely.
An accompanying editorial by David A. Morrow, M.D., M.P.H. of Boston's Harvard Medical School and Brigham and Women's Hospital echoes this sentiment and points to potential problems with sensitive troponin tests. The German study in particular showed that the new tests' ability to identify early on those patients with troponin levels suggesting heart attacks comes at the expense of the ability to identify those chest pain patients who don't have heart attacks, he points out, noting that for every 100 patients in the German study who had troponin levels suggesting heart attack, only 77 were diagnosed with one.
Source: Lab Tests Online US