CRP Test Little Help in Predicting Heart Risk
Blood Protein Linked to Heart Disease Risk but Adds Little Info, Study Shows
March 31, 2004 -- People with high C-reactive protein (CRP) levels are at increased risk of heart disease. But contrary to earlier reports, a large study now shows that CRP tests don't tell your doctor anything new.
At the heart of heart disease, researchers now believe, are runaway immune responses. This "inflammation" theory holds that immune cells attack cholesterol-riddled plaque in blood-vessel walls. The weakened, plaque-filled walls burst, spilling deadly blood clots into the circulation.
Inflammatory immune responses involve a protein called CRP. There's now a simple blood test for CRP. Studies have suggested that high CRP levels independently predict a person's risk of heart disease. In fact, current CDC and American Heart Association guidelines say high-risk patients might well consider getting CRP tests.
Now a much larger study shows that these studies overestimated the value of CRP tests. It confirms that CRP is linked to heart disease risk. But the test doesn't tell doctors anything they don't already know, report John Danesh, MD, PhD, head of the department of public health and primary care at the University of Cambridge, England, and colleagues. The paper appears in the April 1 issue of The New England Journal of Medicine.
"The previous estimates had seriously exaggerated the predictive value of CRP," Danesh tells WebMD. "This study casts serious doubt on its application at the moment. It suggests that translating CRP measurement to clinical practice or screening is probably premature. It is not supported by the best available evidence."
The reason: The newer test adds little to what doctors already know about a person's heart-disease risk from blood cholesterol levels and smoking status.
Danesh's team pored over data on 18,569 Iceland residents studied for more than a decade. They identified nearly 2,500 study participants who had a heart attack or who died of coronary heart disease. That's four times more heart-disease patients than any previous study of CRP. The researchers then compared these patients to some 4,000 participants who did not have a coronary event.
And they went further still. The researchers re-analyzed data from previous studies of CRP and heart disease.
"I think the evidence suggests that blood lipids [cholesterol levels], blood pressure, and cigarette smoking habits provide most of the predictive information that we now have," Danesh says. "The addition of CRP provides comparatively little extra predictive information."