A simple blood test for the protein NT-proBNP accurately predicts the risk of heart attack, heart failure, stroke, and death in patients with known cardiovascular disease, according to a study led by a researcher at the San Francisco VA Medical Center.
The study of 987 men and women with stable coronary heart disease revealed that the higher a patient's level of NT-proBNP, the greater the chance the patient would die or have a cardiovascular event -- heart attack, heart failure, or stroke.
"After adjusting for all other risk factors, it's clear that this marker is picking up something that we are otherwise unable to detect with standard tests such as echocardiography," says principal investigator Mary Whooley, MD, a staff physician at SFVAMC and an associate professor of medicine at the University of California, San Francisco.
NT-proBNP is a marker in the blood for BNP, a hormone that "goes up during times of cardiac stretch or stress," explains Whooley. "When the heart wall is over-expanded by too much blood volume, or damaged by lack of blood flow to the heart itself, BNP goes up, and NT-proBNP along with it."
Patients in the study were divided into four quartiles depending on their NT-proBNP blood levels, and followed for an average of 3.7 years each. Twenty-six percent died or had a cardiovascular event during the course of the study. The study reports that "each increasing quartile ... was associated with a greater risk of cardiovascular events or death." Patients in the quartile with the highest levels of the biomarker were 3.4 times more likely to die or have a cardiovascular event than patients in the group with the lowest levels.
Whooley cautions that the NT-proBNP test is "not something that we should order on every patient who comes in for a routine checkup," but would be most useful for patients with known coronary heart disease. "In the general population, the incidence of heart disease is so low relative to the incidence in heart disease patients that you get many more false positive results than true positives, which really lowers the value of the test," she says. "It's much better at predicting risk in a population with a high incidence of heart disease."
Whooley also notes that, even among heart patients, the value of the test is limited "because all of the therapies available to prevent cardiovascular events should already be used among these patients. The best it can do is help identify candidates for more aggressive therapy."
She says that one additional step for researchers is to see "whether there are therapeutic interventions that still remain to be developed that might prevent heart patients with elevated BNP from doing worse."
Patients in the current study were all enrolled in the Heart and Soul Study, a multi-year prospective study of one thousand heart patients directed by Whooley that is designed to investigate whether depression predicts heart disease. "Because the Heart and Soul Study measures heart disease so carefully, our data set has become extremely valuable for a wide range of cardiovascular studies, many of which have nothing to do with our original hypothesis," Whooley says. "This study is just one example."
The study appears in the January 10, 2007 issue of Journal of the American Medical Association.
Co-authors of the current study were Kirsten Bibbins-Domingo, MD, PhD, and Reena Gupta, MD, of UCSF and San Francisco General Hospital; Beeya Na, of SFVAMC; Alan H.B. Wu, PhD, of UCSF and SFGH; and Nelson B. Schiller, MD, of UCSF and SFVAMC.
The study was supported by grants from the Robert Wood Johnson Foundation, the National Heart, Lung, and Blood Institute, and the UCSF Research Evaluation and Allocation Committee; NT-proBNP assays were funded by Roche Diagnostics Corporation.
The Heart and Soul study is funded by the Department of Veterans Affairs and by grants from the National Heart, Lung, and Blood Institute, the American Federation for Aging Research, the Robert Wood Johnson Foundation, and the Nancy Kirwan Heart Research Fund that were administered by the Northern California Institute for Research and Education.
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