CRP Test for Heart Disease Risk: Valuable, But Not Definitive

A simple blood test that could predict risk for heart disease has been getting a lot of hype lately: “A new test could save the lives of millions who don't even know they're in danger,” announced U.S. News & World Report in a November 2002 cover story. Other reports were equally glowing: “New Test for Risk of Heart Disease; Study Shifts Focus From Cholesterol” said the Washington Post in a nationally distributed story; the Associated Press declared, “Researchers Find a New Enemy of the Heart.”

What’s creating all the buzz is a test for a substance called C-reactive protein, or CRP. It’s not a new test; C-reactive protein was first identified in the 1930s. Nor is it yet the definitive breakthrough in diagnosing risk for coronary artery disease in every patient, says cardiologist David S. Marks, MD, Associate Professor of Medicine at the Medical College of Wisconsin and Director of the Cardiac Catheterization Laboratory at Froedtert & Medical College Clinics. Dr.Marks has been ordering the CRP test on selected patients for several years.

The CRP test, which has been used to detect areas of acute inflammation from diseases such as rheumatoid arthritis and rheumatic fever, is increasingly being utilized in cardiac care. “Patients should know that the C-reactive protein test is not actually a diagnostic test for coronary artery disease but rather a non-specific marker for inflammation,” he says. Even if the test results are positive for inflammation, he notes, the inflammation could be triggered by other factors such as arthritis or an infection; or it could signal the potential for future heart disease.

Some researchers think inflammation can trigger heart attacks by affecting the walls of diseased blood vessels. “There’s no question that C-reactive protein has moved beyond a test for the presence of rheumatic disease,” says Dr. Marks. “We keep learning more about the impact of inflammation and heart disease, but we still don’t know if the C-reactive protein mechanism has a causative effect.”

Cautious Guidelines for Testing
Based on current information, Dr. Marks says not every middle-aged patient should be tested for CRP, “but they should ask their cardiologist or primary care doctor about it.”

In a January article published in the medical journal Circulation, the American Heart Association (AHA) and the Centers for Disease Control and Prevention (CDC) cautiously recommended limited, optional testing for C-reactive protein for patients at some risk for heart disease over the next 10 years based on such factors as age, high cholesterol and high blood pressure – but only if test results will help doctors decide whether the patients need treatment. Treatment typically includes drugs to lower blood pressure and cholesterol, plus lifestyle changes – quitting smoking, eating better diets, exercising, and achieving and maintaining an appropriate weight. Dr. Marks has been following those recommendations with his patients.

“If I’m with a patient who has few risk factors for coronary artery disease but has a strong family history for the disease, I might order the C-reactive protein test.” And if it’s positive, he might start the patient on a preventive program that could include a low-dose aspirin regimen and possibly other drugs, as well as encouraging them to maintain a healthy weight through diet and exercise. “However, if I’m with a patient I already know has coronary artery disease and is taking medication for it and following preventive steps, the CRP test has a different implication.

“It’s always a challenge whenever we introduce a new screening test,” Dr. Marks says. “The AHA and CDC report was cautious, which reflects the fact that physicians still aren’t unanimous in their opinions of the test’s value.” Some fear that widespread use of the test could result in false positive readings, which could raise patients’ anxiety and cost money.

A recent study by Dr. Paul Ridker of Brigham and Women's Hospital in Boston found that half of all heart attacks and strokes occurred in women with seemingly safe cholesterol levels, and that those with high CRP had double the risk of women with low levels.

Prevention Is Still Best
Research into the link between inflammation and heart disease continues. Regardless of the outcome of the research, however, Dr. Marks emphasizes a familiar refrain:

“There’s no substitute for good preventive care. We already know a lot about the risks for heart disease – smoking, high blood pressure, obesity, sedentary lifestyle, diabetes. We don’t need a test to tell us people with these conditions are at risk. These are all modifiable risks that can be managed through lifestyle changes and medication.

“One risk factor that can’t be modified, though, is a family history for heart disease, and the C-reactive protein test can be useful for those patients.”

And, he adds, for patients with established heart disease, the CRP test “may be helpful in showing that the medications those patients are using are effective.”

“The important thing is this,” Dr. Marks says. “The test for C-reactive protein is definitely part of the armamentarium of the physician, and doctors will be using it more and more. It’s not appropriate to test everyone for it right now, but that may change. And it doesn’t alter what we already know about risks that can be modified by the patient and by medication.”

Barbara Abel
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.