Even if people do not have symptoms of heart disease, a new blood test might offer early detection for those who are at risk.
So says a new study published in the Journal of the American Medical Association. Univ. of Texas Southwestern researchers found that a high-sensitivity blood test could point to a protein which indicates heart disease and increased risk of dying, in otherwise healthy individuals.
Researchers said the blood test detected a protein known as cardiac troponin T (cTnT) in about 25 percent of blood samples. Research also showed that people with detectable levels of the protein were almost seven times more likely to die within six years from heart disease.
"The main takeaway here is that there is a new test that can detect microscopic injury to heart muscle cells," said Dr. James de Lemos, associate professor of internal medicine at UT Southwestern and lead author of the study. "The test looks quite powerful and we're optimistic that it will help in the future."
A less sensitive version of the blood test is usually used in emergency rooms to determine if a patient who is experiencing chest pains is actually having a heart attack.
The blood test is not approved for use by the U.S. Food and Drug Administration, but it has been permitted in Europe. De Lemos said that the test is now among the most powerful predictors that has been seen so far, of death in the general population.
"I think this study is really going to resonate with doctors who are interested in prevention," de Lemos said.
Dr. Roger Blumenthal, director of preventive cardiology at Johns Hopkins Medical Institutions, agreed that these findings have the potential to affect clinical practice in the future.
"We're always looking for a new way to identify individuals who are at increased risk of heart attack and stroke," said Blumenthal. "These findings will allow us to motivate patients to improve dietary and exercise habits and better target individuals who are at higher risk in the future."
The protein levels were measured in more than 3,500 study participants, between the ages of 30 and 65. Participants provided blood samples and underwent multiple MRIs and CT scans to examine the heart and other organs. Men were found to be three times more likely to have detectable protein levels than women, and African-Americans had a significantly higher prevalence of the protein than Hispanics or whites.
Study participants were a part of the Dallas Heart Study, a multiethnic population-based cohort designed to estimate biologic and social variables that pinpoint ethnic difference in heart health at a community level.
De Lemos said the Dallas Heart Study was designed to represent urban communities throughout the United States, where there is a high prevalence of obesity, untreated hypertension and diabetes, much like Dallas.
Heart measures like cholesterol and blood pressure indicate problems with blood flow, but elevated troponin levels show problems where the heart muscle has thickened or become weak.
"Heart muscle problems are more important and more dangerous than problems with blood flow in the heart," said de Lemos. "So we're excited by these results compared to other tests."
Blood pressure, cholesterol and glucose blood levels have all become standard measurements and indicators of high-risk patients. Similar to troponin, C-reactive protein, or CRP, is a general marker for inflammation and infection, which can be used as a rough proxy for heart disease risk. But this is not a very specific prognosis since many things can cause an elevated CRP, including bacterial infections, burns and viral infections.
Dr. Robert Bonow, chief cardiologist at Northwestern University Feinberg School of Medicine, said that while important, more work is needed.
"[This study] needs to be reproduced in other large patient registries," said Bonow. "But it certainly could change practice and replace other tests."
Dr. Gordon Tomaselli, president-elect of the American Heart Association and professor of medicine at Johns Hopkins School of Medicine, said that once the study has been reproduced and all is found to be safe and clear, the test could be used in a variety of ways. The measures could be incorporated into a person's overall risk predictor or worked into a person's normal blood work.
But doctors say it is important to note that troponin tests do not measure specifics in the same way that blood pressure and cholesterol tests do. Moreover, if a person is found to have high protein levels, each person must be treated individually.
"What happens next changes from person to person," said Tomaselli. "We may more aggressively treat other risk factors, or if you have blood pressure that is a bit high, we might be more aggressive in treating it with medication or prescribing an exercise program to treat it."
And with more standard testing comes more standard costs. Dr. Gordon Ewy, professor of cardiology and director of the University of Arizona Sarver Heart Center, said that there is always a cost-effectiveness concern when a new medical laboratory test is introduced.
"This is especially relevant during the national debate on health care costs," said Ewy. "It will take some time for physicians to determine when the test should and should not be measured."
Ewy went on to say that the test should not be used on anyone with known renal disease, coronary disease, or congestive heart failure as the test will come out positive and may lead to unnecessary additional tests.
"On the other hand, in asymptomatic individuals, [the test] will probably become an important marker," said Ewy. "Perhaps more important than genetic testing."