DALLAS, Texas, Aug. 25 -- Measuring C-reactive protein with a high sensitivity test may provide a powerful new method to predict risk of heart attack and stroke among healthy post-menopausal women, report researchers in today's Circulation: Journal of the American Heart Association.
According to the scientists, testing for this protein -- which is released into the bloodstream when the blood vessels leading to the heart are damaged -- adds to the predictive value of screening blood samples for both total and HDL (good) cholesterol levels. Thus C-reactive protein testing may improve doctors' ability to predict heart disease risk among women.
"C-reactive protein is a sensitive marker of inflammation, the process whereby the body responds to injury," says Paul M. Ridker, M.D., of Brigham and Women's Hospital and Harvard Medical School, Boston. "When we measure this protein with high-sensitivity test procedures, we seem to be able to detect how much underlying atherosclerosis a patient has and thus predict the risk of future heart attack and stroke events."
In the study, researchers measured C-reactive protein levels in blood samples obtained from participants in the Women's Health Study, an ongoing evaluation of 39,876 healthy, post-menopausal American women.
Overall, women with the highest levels of C-reactive protein had a five-fold increase in the risk of developing any cardiovascular disease and a seven-fold increase in risk of having a heart attack or a stroke, when compared to those with the lowest levels of C-reactive protein.
Levels of C-reactive protein predicted these events even among apparently low-risk women, such as those who did not smoke, had no evidence of high cholesterol and no family history of heart disease.
"These data confirm that increased levels of C-reactive protein are a strong marker of risk not only in middle-aged men, but also in healthy women," Ridker notes.
Last year Ridker and his colleagues reported in the Physicians' Health Study, an ongoing evaluation of 22,000 initially healthy men, that C-reactive protein was a potent predictor of heart attack risk.
"Taken together," he says. "these two studies provide hope that we can do a better job of identifying those at high risk for future heart disease."
In the study of women, levels of C-reactive protein were somewhat higher than previously found in men. The researchers suspect this may be because the women studied were more likely to smoke, weigh more and more likely to have high blood pressure and high cholesterol. It is also possible, they say, that there may be interactions between the inflammatory process and menopause itself.
The researchers caution that standard laboratory tests for C-reactive protein are not sufficient to determine cardiac risk.
"Physicians and their patients need to understand that only 'high-sensitivity' or 'ultrasensitive' tests for C-reactive protein are useful for this purpose," says Ridker. "Perhaps we should be calling this test 'Cardiac-CRP' rather than standard C-reactive protein."
The study was funded by the National Institutes of Health and the American Heart Association.
Co-authors are Julie E. Buring, Sc.D., and Charles H. Hennekens, M.D., of Harvard Medical School; and Jessie Shih, Ph.D., and Mathew Matias, B.S., of Abbott Laboratories, Abbott Park, Ill.