DALLAS, May 26 -- Measuring a certain type of protein in the blood during a common cholesterol test could improve a physician's ability to predict a person's chance of having a heart attack, a new study shows.
Moreover, researchers say measuring for the specific protein -- known as C-reactive protein (CRP) -- would greatly add to the predictability of heart attacks in people not normally seen to be at risk, according to the report in an American Heart Association journal.
Previous studies have shown that people with elevated blood levels of CRP may be at increased risk for a heart attack. CRP is an acute-phase reactant, which means that its levels increase dramatically (100-fold or more) in response to severe bacterial infection, other inflammation or physical trauma.
What was not known previously was whether measuring for that protein adds to the predictive value of tests for blood cholesterol levels.
Scientists examined baseline blood samples among healthy people in the large-scale Physicians' Health Study, based at Brigham and Women's Hospital, and related these levels to the future development of heart attacks over the next nine years. High blood levels of CRP and total cholesterol "were each associated with significantly increased risks of future heart attack," according to the researchers. More important, testing for CRP in addition to total cholesterol proved to be a better predictor of risk than testing for cholesterol alone.
Individuals with elevated levels of both CRP and total cholesterol had a five times higher risk of a heart attack when compared to individuals without either of these risk factors. This risk was substantially greater than the two-fold increase in risk associated with elevated levels of total cholesterol alone.
"The risk of future heart attack among those with high levels of both CRP and cholesterol were greater than the risk of each one combined," says the study's lead author, Paul M. Ridker, M.D., of Brigham and Women's Hospital in Boston. "This raises the possibility that the joint effects of each risk factor may be slightly greater than the individual effects considered separately."
The researchers say this latest finding might be particularly helpful to physicians whose patients do not have many of the common risk factors for heart attack -- cigarette smoking, high blood cholesterol, high blood pressure and physical inactivity.
"We believe that between one-third to one-half of all people who ultimately have a heart attack don't have three or four traditional risk factors," says Ridker. "Such patients may believe they are at low to moderate risk based on a cholesterol profile."
In the current study, which is published in today's Circulation: Journal of the American Heart Association, measurement of baseline CRP proved to be a predictor of risk of first attack in men at low as well as high risk, as determined by cholesterol profiles.
"The fact that markers of inflammation such as CRP are proving to be potent predictors of risk of future heart attack raises the possibility that there may be novel pathways of cardiovascular treatment and prevention directed at the inflammatory process," says Ridker.
In an editorial in the same issue of the journal, Russell P. Tracy, Ph.D., of the University of Vermont, wrote that the same phenomenon may also be true for predicting strokes in otherwise healthy people.
"Taken together, these data suggest that it may be time to add a marker of inflammation to the list of cardiovascular disease risk factors commonly used to assess risk," Tracy wrote.
In addition, Tracy cited prior research that has shown CRP levels to be associated with exposure to cigarette smoke.
"CRP, at least in some people, may mark permanent underlying endothelial (blood vessel) damage due in part to smoking," Tracy wrote. "But it is important to note that in the Physician's Health Study, CRP predicted future events just as well in nonsmokers as in smokers."
The study was funded by the National Institutes of Health. Co-authors are Robert J. Glynn, Sc.D., and Charles H. Hennekens, M.D., both of the division of preventive medicine at Brigham and Women's Hospital.
NR 98-4901 (Circ/Ridker)
Media advisory: Dr. Ridker can be reached through Friday, May 22 by contacting Brigham and Women's Hospital public affairs at (617) 732-5008 and from May 23-25 by calling (617) 732-6660, pager number 13160. (Please do not publish telephone number.)