However, it is not yet a risk factor, such as cholesterol levels or high blood pressure, says the panel convened by the American Heart Association and the U.S. Centers for Disease Control and Prevention (CDC).
The difference between a risk factor and a risk marker might seem trivial, says Dr. Thomas A. Pearson, co-chairman of the panel and senior associate dean for clinical research at the University of Rochester, New York, School of Medicine and Dentistry, but it is critical.
"The difference is that a risk factor not only predicts the disease but also can cause the disease," Pearson says. While many studies show that high blood levels of C-reactive protein are associated with increased risk, there is no evidence thus far that reducing those levels can reduce the risk, he explains.
However, the evidence that high blood levels of C-reactive protein are associated with increased risk of heart attack and stroke is significant enough to warrant giving a test for that marker to individuals already known to be at above-average risk, the panel says.
Their report, published in the Jan. 28 issue of Circulation, says a highly sensitive C-reactive protein (hs-CRP) blood test is appropriate for someone at "intermediate" risk of cardiovascular disease, defined as a person whose health status and history puts him or her at a 10 percent to 20 percent risk of a heart attack in the next 10 years.
"In those cases, an hs-CRP test might tip the scale to help a physician decide on moderate or more intensive treatment," says Pearson. That treatment should be aimed at established risk factors, such as high blood pressure or high cholesterol levels, he says.
Right now, Pearson says, there is "no need for hs-CRP screening of the entire adult population as a public health measure."
And at this time, says a statement by Dr. George A. Mensah, co-chairman of the panel and chief of the CDC's cardiovascular health program, "we have no evidence that treatment strategies based on hs-CRP levels improve survival or reduce cardiovascular complications."
While there is a subgroup of patients that might benefit from hs-CRP testing, the Mensah statement says, "for most patients the emphasis must remain on detection, treatment and control of the major risk factors, such as high blood pressure, high blood cholesterol, cigarette smoking and diabetes."
It's not clear when and if C-reactive protein might be classified as a risk factor rather than just a marker, Pearson says. "Some studies looking at patients who would not be treated ordinarily are under way," he says, but their results will not be known for some time.
The advisory was issued because the hs-CRP test has received so much publicity that many people have asked their physicians for it and there have been no formal recommendations about it, the heart association says. The recommendation is based on current evidence and may be changed as new information becomes available, the panel leaders say.
Perhaps by coincidence, the same issue of Circulation has a report that illustrates the value of the panel's report. Researchers at Harvard Medical School report that CRP blood levels are an excellent indicator of cardiovascular disease for a specific subset of patients, women with the condition called metabolic syndrome. That's the clustering of three or more of five conditions: abdominal obesity, low levels of HDL, or "good," cholesterol, high levels of triglycerides, high blood pressure and high blood sugar levels.
Data on 3,597 participants in the ongoing Women's Health Study showed that those with metabolic syndrome and blood levels of C-reactive protein over 3 milligrams per liter of blood -- the danger level listed in the panel report -- were more than twice as likely to have a cardiovascular event such as a heart attack than women with levels under 1 milligram per liter, the report says.
The study is "the largest ever done that looked at the significance of this marker," says Dr. Nader Rifai, an associate professor of pathology at Harvard Medical School and a member of the research team that has reported several smaller studies. It is also an important as an indication of how the understanding of atherosclerosis, the artery blockage that causes heart disease, has evolved to include inflammation as a significant factor.
Many of the preventive treatments for heart disease turn out to affect inflammation, Rifai says. They include smoking cessation, physical activity, weight reduction and the statin drugs prescribed to reduce blood cholesterol levels. Aspirin, recommended as an anti-clotting agent, is also an anti-inflammatory drug, he notes.
"Maybe in the future we will have more pharmacologic agents available that will reduce inflammation," Rifai says.
You can learn more about inflammation and C-reactive protein in cardiovascular disease from the American Heart Association. Meanwhile, read about women and heart health from the National Heart, Lung, and Blood Institute.