Oct. 10, 2005 - You probably don't need a CRP test to know your risk of a heart attack, a new study suggests.
This doesn't mean it's good to have a lot of CRP -- C-reactive protein -- in your blood. It is not, except when your body is recovering from infection or injury.
But "traditional" risk factors tell most of us when it's time to do more for our hearts, find Michael Miller, MD, director of preventive cardiology at the University of Maryland School of Medicine, and colleagues.
"We can explain the overwhelming majority of coronary heart disease. It is pretty much under our noses," Miller tells WebMD. "We don't need to look for new avenues."
Traditional Risks Tell (Nearly) All
many of us like that? Miller's team tried to find out. Using data from 15,341 men and women enrolled in the National Health and Nutrition Examination Survey (NHANES III), they looked for people with high CRP levels.
They did, indeed, find people whose CRP levels suggested high risk of heart disease. But the vast majority of these people also had other, "traditional" risk factors. Those risk factors:
- High blood pressure
- High levels of bad LDL cholesterol
- High blood-sugar levels, or diabetes
- High blood-fat (triglyceride) levels
- Low levels of good HDL cholesterol
Only 4.4% of men and 10.3% of women had high CRP levels without having at least one of these traditional risks. Although male gender is more often associated with heart disease, women were more likely to have high CRP values.
"If all other risk factors are normal, and you exercise moderately, your risk of having high CRP is one in 2000," Miller says. "A person who is a little overweight, with blood fats and cholesterol a little elevated, maybe with a little bit of high blood pressure -- we didn't used to think that having several of these little risk factors were a big deal. But it is. These little risk factors add up in a way that is worse for you than one big risk factor."
Why CRP Is Important
Miller doesn't think routine screening for CRP is a good idea. But he stresses that what CRP measures is immensely important. In fact, it's the essence of heart disease.
CRP is a marker for inflammation -- the body's first line of defense against infection and injury. When fats build up in the arteries, the body fights them by mounting an immune response. It's a good idea that leads to disaster, says Russell P. Tracy, PhD, Russell P. Tracy, PhD, professor of pathology and biochemistry at the University of Vermont College of Medicine, Burlington. Tracy was part of the team that developed the first test for CRP.
"Because there is a constant infusion of fat particles into the artery wall, the inflammation never goes away," Tracy tells WebMD. "If the blood-fat concentration is high enough, this essentially swamps the system. ... So it is not the fat in the artery that is the problem, it is the immune response to that."
And CRP is, at the moment, the best way to measure this deadly immune response. But since CRP levels are linked to traditional risk factors, Tracy agrees with Miller that not everyone needs a CRP test.
"My opinion is that the public is still best served by finding risk factors a person can work on," Tracy says. "For some people, obesity might be the main risk. For others it might be a high LDL cholesterol level. While knowing CRP and cholesterol ratios might help define the risk, you will have lost the information about the source of the increased inflammation."
Not so fast, says heart disease expert Ishwarlal Jialal, MD, PhD, director of the laboratory for atherosclerosis and metabolic research at the University of California, Davis.
Jialal notes that the Miller study used a relatively insensitive CRP test. This, he says, likely missed a lot of people with dangerous CRP levels but only borderline traditional risk factors. If these people had their CRP measured by current methods, their doctors would be more likely to advise immediate action.
Moreover, Jialal says, monitoring CRP would tell doctors how well treatment -- lifestyle change and treatment with cholesterol-lowering drugs -- is working.
"If you only look at cholesterol and blood fats, you miss the additional risk that CRP portends," Jialal tells WebMD. "CRP is important. And recent studies show when you lower CRP and LDL cholesterol, you have a greater benefit than lowering LDL alone."
More Heart-Risk Tests On the Way
Tracy says there's another reason not to put too many eggs in the CRP basket. CRP, he notes, is only one of thousands of blood proteins involved in heart disease.
Researchers now are beginning to translate the eloquent language spoken by these chemical messengers. Until more is known, Tracy says, it's not a good idea to bet scarce public-health dollars on the first horse in the race.
"We are making huge strides in understanding this disease," Tracy says. "We should be prepared to change as our knowledge explodes. With this will come new methods for the prediction, diagnosis, and treatment of heart disease. So let's keep the enthusiasm, and use CRP wisely when it really can help doctors make a change for a patient. And let's keep our ears to the ground for the changes that will happen in the next five to 10 years."