What's the Usefulness of CRP Testing?
Measuring C-reactive protein in the blood may -- or may not -- indicate that a person is at risk for heart disease.
Reviewed By Brunilda Nazario
By now, most of us are well-versed in the rules for keeping heart disease at bay: eat healthily, exercise, don't smoke or gain too much weight, and keep blood pressure and cholesterol levels under control. And familiarity with terms like HDL and LDL cholesterol is so common as to make for standard cocktail party chitchat.
But there's a lesser-known, relatively new player in heart-disease risk assessment called CRP, or C-reactive protein. A study in the January 2004 issue of The New England Journal of Medicine suggested that elevated levels of CRP could provide doctors with information that could ultimately prevent thousands of deaths from heart disease. But many reports have said that knowing CRP levels provides no clinical benefit whatsoever, making the whole subject a source of controversy.
The blood test for CRP indicates inflammation, which studies have shown to be critical in the development of atherosclerosis, or plaque build-up in the blood vessel walls.
According to the American Heart Association and the CDC, a CRP level of less than 1 mg per liter indicates a low risk of cardiovascular disease; 1-3 mg/L indicates moderate risk, and greater than 3 mg/L equals high risk.
But while the test itself is simple, its implications can be confusing.
"I don't think anybody disputes that inflammation plays an important role in artherosclerosis and its complications," says P.K. Shah, MD, director of cardiology at Cedars-Sinai Medical Center. "But the incremental value of CRP as a risk factor above all the conventional risk factors is relatively small. This is the biggest bugaboo about CRP -- we don't know what to do with the information."
One problem with the CRP test is that it's not specific, so levels can be elevated due to other sources of inflammation besides artherosclerosis, such as gum disease or a viral infection. (For this reason, if you do want to be tested for CRP, doctors recommend waiting if you have an acute infection.)
Another issue is what exactly a patient should do if he is found to have a high CRP level. Lowering CRP levels doesn't necessarily reduce risk of heart disease.
CRP Test Not Recommended for Everyone
If you've got other risk factors for heart disease, you're most likely already taking a cholesterol-lowering drug and aspirin therapy, and are on lifestyle-changing programs such as routine exercise and weight loss to prevent heart disease.
"Knowing your CRP level in this case wouldn't change a doctor's recommendations," Robert Ostfeld, MD, MS, tells WebMD. Ostfeld is a cardiologist at Montefiore Medical Center in Brooklyn, N.Y. Statin drugs as well as standard lifestyle changes used to lower cholesterol have been shown to lower CRP levels as well, but it's not clear that having a high CRP level yet having other factors that only place you at a "low to moderate" risk for future heart disease warrants treatment with a statin. An ongoing study known as the JUPITER trial is trying to address this very issue.
CRP testing might be useful when a doctor is undecided about how aggressively to treat a patient who is considered to be at 'intermediate' risk for a heart attack (meaning having a 10% to 20% risk for heart attack in the next 10 years based on his or her health status and history). In such a case, elevated CRP levels might cause a doctor to decide on more intensive treatment than he would have without CRP results.
Currently, CRP testing is not recommended for the general population. "But it's being pushed and pushed, and people are being led into believing that CRP is a lifesaver for everybody and it's just not," says Shah, who routinely receives requests from his patients for the test. "Patients are often misled into believing that all of a sudden there's this unique marker that's going to determine whether they live or die."
Shah calls the test an interesting but not yet clinically usable tool. "If future studies show that even if all other risk factors are under good control but CRP is high and that that lowering CRP is going to create clinical benefit, then there would be a reason to measure CRP, but we don't have that information yet," he says.
"I'm not saying that five years from now when we have more data we won't change our recommendations," he tells WebMD. "We should keep our eyes and ears opened for more information before jumping on the bandwagon."
The bottom line? Stay tuned.
Published Feb. 7, 2005.
SOURCES: P.K. Shah, MD, director of cardiology, Cedars-Sinai Medical Center, Los Angeles. Robert Ostfeld, MD, MS, attending cardiologist, division of cardiovascular medicine, Monefiore Medical Center, Brooklyn, N.Y.
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