Blood Protein Signals Heart Disease Risk

As cholesterol builds up on artery walls, blood vessels shrink and blood pressure goes up. Now, there's a new test to help predict dangerous ruptures in those clogged arteries -- ruptures that can lead to heart attack or stroke.

The cheap, easy blood test measures circulating levels of an inflammation-linked compound called C-reactive protein (CRP), and it's becoming increasingly popular in doctor's offices nationwide.

"Even people with relatively low cholesterol levels, if they have a high CRP they may still be at high risk for heart trouble," said Dr. James O'Keefe, a spokesman for the American College of Cardiology and director of preventive cardiology at the Mid-America Heart Institute in Kansas City.

Another expert, former American Heart Association president Dr. Sidney Smith, stressed that the CRP screen should complement -- not replace -- traditional diagnostic tests such as screens for cholesterol and high blood pressure.

"At this point in time, it looks as if it will provide important additive information -- additional data that will be very helpful," he said.

Smith, director of cardiovascular science and medicine at the University of North Carolina at Chapel Hill, was also a co-author of heart association recommendations on CRP screening, issued in 2003. At that time, the group advised "against screening of the entire adult population for [CRP]." Instead, it recommended doctors use the test at their own discretion, noting that it is probably most useful in patients already diagnosed with various risk factors for heart disease.

CRP is a marker of inflammation, the process by which the body responds to injury and disease. As arteries get clogged with cholesterol and placed under increasing strain, inflammation often occurs.

"It may be that CRP helps cause the inflammation, but mostly it's a marker for it," O'Keefe said. CRP isn't restricted to heart disease -- in fact, it's found at relatively high levels in people with chronic inflammatory illnesses such as rheumatoid arthritis or inflammatory bowel disease.

However, "we've learned over the past decade that the process of atherosclerosis [hardening of the arteries] develops over years, and that inflammation seems to be a very important part of causing the atherosclerotic lesion to ulcerate and then 'clot off,' " Smith said. "So it's this combination of the atherosclerotic process and the presence of an active inflammatory state that seems to identify people that are at higher risk."

O'Keefe agreed. "I like to use the analogy of a pimple on your skin," he said. In pimples, as in diseased arteries, inflammation swells the affected tissue -- often to the bursting point.

Of course, when pimples burst, the effects are mostly cosmetic and fleeting. But when inflamed arteries burst, "it exposes [fatty] material and sends it into the bloodstream, making the blood more likely to clot -- and that's how a heart attack happens," O'Keefe said.

That's why the CRP test -- which costs about $12 -- may be especially helpful for patients already at high cardiovascular risk due to factors such as high blood cholesterol, hypertension, obesity, smoking, or a family history of heart disease.

Like the heart association, the American College of Cardiology has yet to designate the CRP test as a standard, first-line screen for heart disease, but O'Keefe said that "as more and more information comes out, I'm sure they will in the near future."

He pointed to two separate articles, published this January in the New England Journal of Medicine. Both studies found that "elevated CRP is as strong a predictor as LDL 'bad' cholesterol, in predicting who's going to get heart trouble," O'Keefe said.

Even individuals with low cholesterol might benefit from the CRP test, O'Keefe added.

"There's data to suggest that [patients with high CRP] can reduce their risk for heart attack by treating their already low cholesterol with a statin drug, to lower it further. Because statins also lower inflammation, as well," he said.

Most Americans may not need to turn to drugs to lower arterial inflammation, however, since the very behaviors that drive up cholesterol and high blood pressure -- smoking, lack of exercise and poor diet -- appear to send CRP skyward, too.

"The most important risk factor of all is obesity," O"Keefe warned. "Chronic excess weight, especially around the midsection, increases C-reactive protein. Lean people tend to have lower CRP, so my advice is to exercise more, lose weight, and eat a healthy diet."

More information

To learn more about CRP, visit the American Heart Association.