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CRP: A new test for heart disease risk

Though it's known that high cholesterol causes heart disease, only about half of people who have heart attacks have high cholesterol. That's one reason why researchers are searching relentlessly for other tests that can forecast a person's chances of developing heart disease. One test on the brink of mainstream use measures a substance called C-reactive protein, or CRP for short.

Predictive protein

In healthy people, only small amounts of CRP circulate in the bloodstream. At the first sign of serious injury or infection, though, the liver starts churning out more. Although the protein's exact function is still something of a mystery, doctors have used it for years to monitor diseases such as pneumonia, rheumatoid arthritis, and lupus.

The idea that inflammation - the same process that triggers a fever or causes swelling around a cut or injury - might be at the heart of atherosclerosis led researchers to take another look at CRP. Could small but persistent elevations in CRP levels indicate the low levels of chronic inflammation that reflect unhealthy changes in artery walls?

Supersensitive tests for CRP developed in the early 1990s made it possible to test this hypothesis. A gush of studies has shown that as the CRP level rises, so does the risk of having - or dying from - a heart attack, stroke, or other cardiovascular problem.

Hurdles to jump

Before CRP testing goes mainstream, two key pieces of the puzzle need to be found. First, no one knows whether lowering CRP levels actually makes a difference. If the protein is just a marker or stand-in for one of the real culprits behind atherosclerosis, then lowering it could be like treating measles by covering the skin rash with makeup.

The second big unknown is whether starting statin therapy in response to a high CRP level is better than starting it based on a high LDL level. Studies are currently underway to answer this question.

Is CRP for you?

Until we know more about what high and low CRP levels really mean, not everyone needs to have this test. Here are some guidelines:

  • Don't bother if you are already being treated for heart disease or high cholesterol. The results of a CRP test won't change how you and your doctor manage your condition.
  • Think about it if your cholesterol levels are okay but you have other signs that heart trouble could be in your future, like a family history of heart disease, high blood pressure, or diabetes.
  • If you have arthritis, inflammatory bowel disease, or some other condition that causes inflammation and thus elevates CRP, the test for this protein might not tell you much about your future chances of developing heart disease.

Dealing with high CRP

A high CRP level isn't a disease. It's really a symptom, like a fever, that signals something's amiss and needs tending. If your CRP suggests a high risk of heart disease (see table), you may want to pay extra attention to heart-healthy habits. Losing weight, stopping smoking, and exercising all help prevent heart disease. Each of these also lowers CRP, though whether that's part of the protective effect is anyone's guess.

Your doctor may suggest that you take a daily aspirin, since this drug offers the greatest protection against heart attack in people with high CRP. He or she may also want you to take a statin, even if your cholesterol is in the normal range. These drugs can cool inflammation and stabilize plaque.

C-reactive protein and cardiovascular risk

CRP level

Cardiovascular risk

Below 1 mg/dL

Low

1-3 mg/dL

Moderate

Above 3 mg/dL

High (about twice the risk as someone with a CRP below 1)

February 2004 Update

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