CRP: A new test for heart disease
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.
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
C-reactive protein and cardiovascular
Below 1 mg/dL
Above 3 mg/dL
High (about twice the risk as someone with a
CRP below 1)
February 2004 Update
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