Findings from a large study suggest the simple blood test may be an even better predictor of heart attack or stroke risk than cholesterol levels. The American Heart Association and the CDC plan to issue a joint statement on its clinical use soon, but experts say it is still not clear whether routine testing is needed.
"I think most of us in the field are quite excited by this, but there are still many unanswered questions," cardiologist Lori Mosca, MD, PhD, tells WebMD. "This marker appears to predict future [heart] events, independent of other risk factors. The limitation is that we don't yet know if lowering C-reactive protein levels lowers one's risk of heart disease."
In recent years, researchers have found that blood vessels in people with heart disease have inflammation. C-reactive protein (CRP) is released into the blood in response to this inflammation. Although previous research has shown elevated CRP levels to be predictive of heart attack and stroke, these studies were mostly small and had short follow-up times.
In this study, researchers from Boston's Brigham and Women's Hospital measured CRP and LDL "bad" cholesterol levels in close to 28,000 women. Their findings are published in the Nov. 14 issue of TheNew England Journal of Medicine.
After following the women for eight years, they found that CRP was superior to LDL cholesterol for predicting risk of heart attack, stroke, and sudden death due to heart causes. This held true even after adjusting for known risk factors of heart disease, such as smoking, older age, and diabetes.
In fact, women with high CRP but low cholesterol levels were at higher risk for heart attacks and strokes than those who had high cholesterol levels but low CRP, according to lead researcher Paul M. Ridker, MD.
The findings add to the evidence that low-grade inflammation within the body is a leading cause of heart disease. It is believed that such inflammation leads to the weakening and eventual rupture of artery-clogging plaques, which cause heart attacks and strokes.
"This data represents a fundamental shift in our thinking about [heart] disease and its prevention," Ridker says. "It is no longer acceptable for physicians to focus solely on cholesterol since the evidence is overwhelming that those with low cholesterol but high CRP are in fact a very high-risk group."
Study co-researcher Nader Rifai, PhD, tells WebMD that since CRP and LDL are independent predictors of heart disease, the two blood tests can be used together to better identify those at risk. Of the women in the study who eventually had heard disease, more than half had cholesterol levels that were considered normal.
"This test should be given routinely," Rifai says. "It will help clinicians identify a group of individuals who are at increased risk for heart disease, who otherwise would be missed."
But American Heart Association president Robert O. Bonow, MD, tells WebMD that the jury is still out on whether CRP testing represents a major advance for the identification of people in danger of having heart attacks and strokes. The role of CRP in clinical practice will be the focus of a special session next week during the AHA's annual scientific meeting in Chicago.
"This marker doesn't really tell us much about people who are at very high risk or very low risk for [heart attack or stroke]," Bonow says. "Its real value may be in people who are on the borderline of needing treatment."
Bonow notes that CRP levels tend to mirror heart risk factors linked to lifestyle. In other words, if you have a healthy lifestyle your levels will probably be low. People who smoke, don't exercise, and/or are overweight are more likely to have high CRP levels.
"It has never occurred to me to have my CRP checked, even though I have a family history of heart disease," says Mosca, who wrote an editorial calling for more testing on the value of CRP. "I'm sure it is just fine because I exercise, eat well, maintain a good body mass index and have an occasional glass of wine."