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."
Still Not Enough Information
What the new findings don't mean is that doctors can find out all they need to know about a person's risk of heart disease. While CRP adds little new information, there's a tremendous need to know more, notes Alan Tall, MD, director of the specialized center for research in atherosclerosis at New York's Columbia University. Tall's editorial accompanies the Danesh study in the NEJM.
"Unfortunately, we are not making that much progress in getting new markers in the blood or genetic markers that allow us to predict who will get heart disease and who won't," Tall tells WebMD. "So the way we are going is simply to treat more people. Our ability to define who will most benefit from treatment is sadly lacking. The evidence is we should be treating more people more aggressively and that is the way we are going."
Current treatments for heart disease risk come in two flavors. The first is lifestyle change, meaning more exercise and a low-fat, reduced-calorie diet. The second is cholesterol-lowering drugs. High-risk patients will likely need both, but lifestyle change can keep most people from becoming high-risk patients in the first place.
Meanwhile, Danesh's team is going through the data with a fine-tooth comb to see whether there are subgroups of patients who might benefit from CRP screening.