Common Heart Failure Test May Be Flawed
New finding could change treatment for the condition
MONDAY, Nov. 14, 2005 (HealthDay News) -- A standard diagnostic test for heart failure is wrong in a subtle way that could lead to harm for some patients, researchers report.
The test measures levels of brain natriuretic peptide (BNP), a hormone produced by heart muscle. More BNP is produced in heart failure because the heart progressively loses its ability to pump blood and then strains to get the work done. That's why cardiologists routinely measure BNP levels as they diagnose and treat the disease.
However, the body makes different forms of BNP, noted lead researcher David C. Muddiman, a professor of chemistry at North Carolina State University in Raleigh. One is the "active" form, made under normal conditions, while another form is produced when the heart starts to fail.
According to Muddiman's team, the standard test doesn't distinguish between those two forms.
Using a high-tech method called mass spectrometry, "Our data shows for the first time that they are not measuring what they think they are measuring," he said. "They are not measuring the active form, the form that helps you."
The findings appear in this week's online issue of the Proceedings of the National Academies of Science.
The difference can be crucial in some cases, because heart failure is often treated by giving the patient the active form of BNP using a drug called Natrecor, Muddiman said.
"In some patients who have high BNP levels, maybe it's the active form, [so] when you give them the active form, they have way too much," he said. "If the measurement shows they are making the active form, you wouldn't have to treat the patient so aggressively."
The study is already having an effect on treatment of heart failure at the Mayo Clinic, said study co-researcher Dr. John C. Burnett Jr., director of the cardiovascular research center there.
"There is no question that we need to rethink how much BNP we give patients," Burnett said. "Here at the clinic, we now give half the recommended dose."
The study still supports the use of Natrecor to treat heart failure, he said. "If a lot of the BNP that is circulating is the junk form, that justifies the strategy to use real BNP to treat heart failure," he said.
A patient's blood level of BNP measured by the standard test is less important than that patient's response to Natrecor, Burnett said. Giving the smaller dose allows the physician to monitor the patient's reaction and to adjust the dose accordingly, he said.
More must be done to learn about the levels of the different forms of BNP in heart failure patients, Muddiman said. "If we can understand that a certain part of the population is actually making the right hormone, that would be great," he said. "That is what we are trying to do now. We are recruiting lots of patients."
Find out more on heart failure at the American Heart Association.