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Study Questions Widespread Use Of C-reactive Protein Test To Assess Cardiovascular Risk

Date:
October 12, 2005
Source:
University of Maryland Medical Center
Summary:
A new study concludes that widespread screening for cardiovascular risk by measuring blood levels of C-reactive protein (CRP), a protein produced by the liver, should not be advocated, because CRP appears to be tightly linked to traditional risk factors for heart disease rather than being an independent risk factor.
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A new study concludes that widespread screening for cardiovascularrisk by measuring blood levels of C-reactive protein (CRP), a proteinproduced by the liver, should not be advocated. Researchers at theUniversity of Maryland School of Medicine in Baltimore analyzed datafrom more than 15,000 adult men and women and found that CRP appears tobe tightly linked to traditional risk factors for heart disease ratherthan being an independent risk factor. The study is published in theOctober 10, 2005, Archives of Internal Medicine.

C-reactive protein (CRP) is released by the liver in response toinflammation related to an infection, injury, or conditions such asarthritis. Inflammation also has been associated with the cause andprogression of cardiovascular disease, particularly in the build up offatty deposits in the lining of arteries.

The researchers found that elevated CRP goes hand in hand withtraditional risk factors for heart disease, such as smoking, obesity,high blood pressure or elevated cholesterol, and rarely occurs in theirabsence. CRP levels are defined as normal (less than 1 milligram perliter (mg/L), borderline-high (1-3 mg/L) and high (greater than 3mg/L).

"We believe that high C-reactive protein is truly related to thecompany it keeps," says principal investigator Michael Miller, M.D.,director of preventive cardiology at the University of Maryland MedicalCenter and associate professor of medicine at the University ofMaryland School of Medicine. "The CRP test gained popularity in thelate 1990's when it was believed that only 50 percent of heart attackscould be explained by traditional risk factors," says Dr. Miller."However, this turned out to be one of the greatest myths incardiovascular medicine as recent studies have affirmed that more than90 percent of heart attacks can be accounted for by traditional riskfactors, as well as poor diet, sedentary lifestyle and mental stress."

Dr. Miller and his team examined data from the third National Healthand Nutrition Examination Survey (NHANES III) conducted between 1988and 1994. NHANES III measured CRP levels and heart disease risk factorsincluding smoking, elevated blood pressure and cholesterol levels,diabetes, body mass index and physical activity.

"We looked at high CRP and compared its prevalence with and withoutother risk factors for heart disease," says Dr. Miller. Overall, 25.7percent of the people in the study had elevated CRP, including 8.7percent who had no other risk factors. African-Americans had higher CRPlevels than Caucasians. The analysis found a high CRP level in 77.8percent of men and 66.7 percent of women who had at least one riskfactor for heart disease.

The presence of at least one of those risk factors, either in theborderline or abnormal range, resulted in a nearly three-fold higherprevalence of CRP compared to people in the study who never smoked,were not overweight and had normal blood pressure, cholesterol andblood sugar levels. "The surprising finding in our analysis was thevery high percentage of elevated CRP that was directly attributable toconventional risk factors," says Dr. Miller.

A look at body mass index in the NHANES III survey illustrates how riskfactors can influence CRP levels. The index can indicate whether aperson is obese, overweight, underweight or normal. CRP levels wereprevalent in 14.7 percent of people with a normal body mass index, butwere found in 26 percent of people who were categorized as overweight.The percentage jumped to 46.6 percent among people whose body massindex put them in the obese range.

Numerous experts have been debating the use of the relativelyinexpensive CRP blood test as a general screening tool for coronaryheart disease, both pro and con. Some say CRP can help identify certainpatients at risk for heart disease that other measurements, such ascholesterol, may miss, so they recommend that the test be given topeople even if they are at low risk for cardiovascular disease.

However, in 2003, the American Heart Association and the Centers forDisease Control and Prevention issued a joint scientific statement thatrecommended against the general screening of the adult population forCRP. Instead, the statement said that CRP measurements should bereserved for patients at intermediate risk for heart disease, who havea 10 to 20 percent risk of developing the disease over ten years. Thestatement also called for additional studies of the CRP test.

Dr. Miller believes that CRP screening is unlikely to contributesufficient insight beyond traditional risk factors and may even becounterproductive. "The great concern of CRP screening is that it mayprovide false assurance to men and women who may be at increased riskof a heart attack despite normal CRP levels," says Dr. Miller. "Becausethe majority of people at risk for a heart attack do not have high CRP,normal levels at screening may make obese patients or smokers, forexample, less motivated to lose weight or kick the habit." On the otherhand, according to Dr. Miller, if a high CRP is found on routinescreening, then therapies that reduce high blood pressure, glucose,cholesterol and triglycerides will also lower CRP. "We should be makingthese adjustments anyway, regardless of CRP levels," he adds.

Dr. Miller says the good news is that in the absence of risk factors,high CRP is very rare. "If you exercise, don't smoke, have normallevels of blood pressure, cholesterol and glucose and are notoverweight, the likelihood of having a high CRP is only one in 2,000,"he says. Rather than screening for CRP, Dr. Miller says "Let's workmore intensively to reduce the known culprits, such as obesity anddiabetes, which are growing to epidemic proportions and have become amajor public health concern in the U.S. Otherwise, we run the risk oferasing the great advances that have contributed to the reduction incardiovascular disease during the past 40 years."

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The research team also included Min Zhan, Ph.D. and Stephen Havas,M.D., M.P.H., M.S., both of the University of Maryland School ofMedicine. The study was supported in part by a National Institutes ofHealth grant and a Veterans Affairs Merit Award to Dr. Miller.


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Materials provided by University of Maryland Medical Center. Note: Content may be edited for style and length.


Cite This Page:

University of Maryland Medical Center. "Study Questions Widespread Use Of C-reactive Protein Test To Assess Cardiovascular Risk." ScienceDaily. ScienceDaily, 12 October 2005. <www.sciencedaily.com/releases/2005/10/051011073102.htm>.
University of Maryland Medical Center. (2005, October 12). Study Questions Widespread Use Of C-reactive Protein Test To Assess Cardiovascular Risk. ScienceDaily. Retrieved March 29, 2024 from www.sciencedaily.com/releases/2005/10/051011073102.htm
University of Maryland Medical Center. "Study Questions Widespread Use Of C-reactive Protein Test To Assess Cardiovascular Risk." ScienceDaily. www.sciencedaily.com/releases/2005/10/051011073102.htm (accessed March 29, 2024).

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