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By Melissa Tennen, HealthAtoZ writer
New guidelines for a blood test may help doctors determine your risk for heart attack and stroke.
Blood levels of C-reactive protein (CRP) can help doctors decide if you need treatment and what you need to do to stay healthy.
The guidelines, issued by the American Heart Association and the Centers for Disease Control and Prevention, answer some questions raised by patients and their doctors concerning new studies on CRP's role in predicting heart disease. Some 40 million people could be eligible for the test.
"It's ideal for someone who is at intermediate risk. It can tip the balance to help a physician decide on moderate or more intensive treatment," says Thomas A. Pearson, M.D., co-chairman of the panel which determined the guidelines and senior associate dean for clinical research at the University of Rochester in New York. "But we urge very limited use of this test. There is no evidence that says everyone should be tested. This should be an optional adjunct."
CRP is a protein that increases in the blood when there's inflammation of blood vessels. Inflammation occurs when there has been an injury or the body is fighting an infection. The inflammatory process can help cause atherosclerosis, a build up of fatty deposits in the lining of arteries.
Intermediate risk means you have some risk factors for cardiovascular disease, such as borderline cholesterol levels along with a sedentary lifestyle. Other risk factors include being overweight, smoking, having a strong family history and eating a high-fat diet. Someone at high risk would be put on an aggressive treatment, which might include cholesterol medications, for example. The CRP test would not be necessary for someone at high risk. Yet someone who might have elevated levels of CRP but no other risk factors would not need to be tested, according to Pearson.
A person is considered at intermediate risk, if he or she has a 10 percent to 20 percent chance of a heart attack in the next 10 years.
"The guidelines provide a framework to help guide physicians," says Lori Mosca, M.D., M.P.H., Ph.D., associate professor of medicine and director of Preventive Cardiology at Columbia University in New York.
The conservative guidelines are intended to keep medical costs down and protect patients from false alarms.
"I've heard of some people getting cardiograms, angiograms and stress tests who have high CRP levels and are at very low risk. These tests cost thousands of dollars," Mosca says.
Scientists have been aware of this protein's existence for more than 70 years, and that it appears in the blood during all types of infections. Researchers have only recently started to try to understand its role in cardiovascular disease, says Iftikhar J. Kullo, M.D., F.A.C.C., consultant in the Division of Cardiovascular Diseases and Internal Medicine and assistant professor in medicine at the Mayo Medical School and Mayo Clinic in Rochester, Minn.
"High levels of CRP may help in predicting the overall risk of a heart attack," Kullo says. "However, given our current knowledge, CRP is not a risk factor but a risk marker. Cholesterol, on the other hand, is a risk factor. We don't have the same information about CRP as we do with cholesterol. What would be helpful is to do a clinical trial with a medication that lowers elevated CRP levels but does not affect other factors in the blood. But we don't have that yet."
In a 1997 study published in the New England Journal of Medicine, researchers found that blood levels of CRP are elevated many years before a heart attack or stroke. Researchers learned that men in the study with highest levels of CRP had a threefold increase in their risk of heart attack and a twofold increase in their risk of stroke compared with men who have lower levels. And elevated levels predicted heart attacks as many as six to eight years in advance.
In a recent study of 27,000 women participating in the ongoing Women's Health Study, an elevated level of CRP was a better predictor of risk for future cardiovascular events than elevated low-density lipoprotein cholesterol, the bad cholesterol.
The panel, Pearson says, looked at "tens of thousands" of CRP blood tests collected in the last two years before making its conservative guidelines.
Finding elevated CRP levels in someone who is at intermediate risk could help change their behavior.
"A possible use of CRP testing is to help doctors motivate patients further. Doctors might say, 'Your CRP level is high and losing weight and quitting smoking would help to lower it.' The high levels of CRP can help us make a particular patient more aware of his overall risk," Kullo says.
Doctors still don't know for sure if lowering CRP using cholesterol-lowering medication will result in lowering the risk for heart attack or stroke, Kullo says. It is also not proven that treatment decisions based on CRP testing would be cost-effective.
Heart Attack Warning Signs
Some heart attacks are sudden and intense -- the "movie heart attack," where no one doubts what's happening. But most heart attacks start slowly, with mild pain or discomfort. Often people affected aren't sure what's wrong and wait too long before getting help.
Here are some signs of a heart attack from the American Heart Association. If a loved one has any of these signs, call 911 immediately:
- Chest discomfort. Most heart attacks involve discomfort in the center of the chest that lasts more than a few minutes, or that goes away and comes back. It can feel like uncomfortable pressure, squeezing, fullness or pain.
- Discomfort in other areas of the upper body. Symptoms can include pain or discomfort in one or both arms, the back, neck, jaw or stomach.
- Shortness of breath. This feeling often comes along with chest discomfort. But it can occur before the chest discomfort.
- Other signs. These may include breaking out in a cold sweat, nausea or lightheadedness
Stroke Warning Signs
Stroke is the third most common cause of death, after heart disease and cancer, and a leading cause of serious disability, according to the American Stroke Association.
- Sudden numbness or weakness of the face, arm or leg, especially on one side of the body.
- Sudden confusion, trouble speaking or understanding.
- Sudden trouble seeing in one or both eyes.
- Sudden trouble walking, dizziness, loss of balance or coordination.
- Sudden, severe headache with no known cause.
Cardiac arrest strikes immediately and without warning.
Here are some signs:
- Sudden loss of responsiveness. No response to gentle shaking.
- No normal breathing. The victim does not take a normal breath when you check for several seconds.
- No signs of circulation.
- No movement or coughing.
This article was reviewed and updated June 2007.
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