An improved version of a blood test can better determine who hasn't had a heart attack among people coming to the emergency room with symptoms such as chest pain, according to a new study published in The Lancet. The study evaluated a highly sensitive version of a blood test that measures troponin, a protein released into the blood when there is damage to heart muscle—which is what happens during a heart attack.
Quickly ruling out heart attacks with greater accuracy could have significant impact on healthcare in the U.S. Every year about five million people go to emergency rooms complaining of chest pain, according to the American Heart Association.
The improved high-sensitivity troponin tests detect the same protein that the standard troponin tests do, but at much lower levels. None of these newer high-sensitivity troponin assays are yet available in the U.S., but research is ongoing and they may become available in the near future.
Standard troponin tests are currently used in emergency rooms to check patients with chest pain or other symptoms for a heart attack, and a high level of troponin confirms it. But low or undetectable levels do not necessarily mean that the patient is not having a heart attack and the patient is sometimes asked to stay so that the test can be repeated to see if troponin levels are rising. Many are ultimately discharged not having had a heart attack, but only after unnecessary hours spent in the hospital.
In the recent study, the highly-sensitive troponin blood test was used to measure troponin levels in over 6,000 patients with chest pain at three hospitals in Scotland and one in the U.S. The researchers checked in with patients a year after they were sent home from the hospital. They found that a troponin of less than 5 nanograms per liter (ng/L or 0.005 ng/mL) was a level that identified patients with a three times lower risk of a heart attack or death from heart disease than patients who had a higher troponin level in the study. Using this cut-off would not be possible with conventional troponin assays, whose lower limit of detection is much higher.
These patients (who represented two-thirds of the total) could probably have been discharged immediately and safely from the emergency room. The researchers found that the cut-off could be used for discharge regardless of age, gender, other risk factors for a heart attack, or a previous indication of heart disease.
"Until now there were no quick ways to rule out a heart attack within the emergency department," says Anoop Shah, MD, the lead author of the study and a clinical research fellow at the University of Edinburgh. Previous studies have hinted at this possibility, but this study is the first to use a large enough number of patients to firmly establish a reliable cut-off.
However, more studies are needed before that threshold can become common practice, say researchers from New Zealand and Australia who commented on the study in the same issue of The Lancet. The commentators point out, for example, that individual patient factors still need to be considered before discharging patients after the single troponin test.