Intermediate CV risk overestimated in Americans.
It's most often claimed that about 40% of American adults are at in termediate risk for coronary heart disease. But this turns out to be a very soft figure that's not even close to the estimate derived from the National Health and Nutrition Examination Survey (NHANES), which provides the most comprehensive available picture of the nation's cardiovascular risk factor status.
NHANES data from 1999-2000 suggest the true figure is not 40%, but rather just 5.5% (9 million) of Americans aged 20-79 years at intermediate risk of cardiac death or nonfatal MI within the next 10 years, said Dr. Keevil of the department of medicine at the University of Wisconsin, Madison.
This finding has important implications for health policy and financing. National Cholesterol Education Program (NCEP) guidelines recommend categorizing all adults as at low, intermediate, or high risk for cardiovascular events. It's the intermediate group that's considered for coronary artery calcium measurement and other noninvasive testing aimed at further risk stratification.
"For those who are planning programs involving methods of improved risk prediction, I think you need to anticipate smaller participation estimates. And for people within policy decision-making bodies that are concerned about the high cost of these developing risk tools, the potential for a lower population impact may actually be somewhat reassuring," Dr. Keevil said.
The NHANES data set represents 166 million American adults aged 20-79 years. Dr. Keevil, an engineer and computer scientist as well as a preventive cardiologist, determined the number of standard cardiovascular risk factors as well as the Framingham risk score for each survey participant. Using the standard NCEP definition of intermediate risk--two or more risk factors plus a Framingham score of 10%-20%--he calculated 5.5% of adults qualify.
If a broader definition, as advocated in the ACC's 34th Bethesda Conference in 2002, is used--that is, at least two risk factors plus a Framingham score of 6%-20%--then the intermediate-risk group grows to 10.1%, or 16.7 million individuals. And using the most liberal definition of all--not even bothering to count risk factors, and instead labeling everyone with a Framingham score of 6%-20% as intermediate-risk--then 16.2% qualify.
"I would argue that the liberal criterion is a little too liberal. Here's my case: Take a 59-year-old man with a blood pressure of 120/70 mm Hg, no blood pressure medications, a body mass index under 25, triglycerides of 120 mg/dL, a total cholesterol of 150 mg/dL, an HDL of 45 mg/dL, and an LDL of 81 mg/dL. No strong family history. No tobacco use. I think most people--in particular, most men age 59 and older--wouldn't mind that risk profile at all. At age 59, however, your Framingham score starts at 6%. This is why I would suggest we not send every male 59 and over for calcium screening and other noninvasive tests," he explained.
Conventional wisdom holds that 25% of the adult population is at high risk, meaning they have known coronary disease, a CHD risk equivalent such as diabetes or peripheral artery disease, or a Framingham score greater than 20%. That 25% figure--like the 40% prevalence of intermediate risk cited in an influential article by Philip Greenland, M.D., and colleagues (Circulation 2001;104:1,863-7)--also appears to be too high, in Dr. Keevil's estimation. On the basis of NHANES data, which included ankle-brachial index measurements in all participants, the true figure is 16.4%, or 27 million Americans.
That means the combined total number of truly intermediate- and high-risk adults is 36 million, or roughly the same as the number described as being high risk in most of the recent medical literature, Dr. Keevil noted.
BY BRUCE JANCIN
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|Title Annotation:||Clinical Rounds|
|Publication:||OB GYN News|
|Date:||Apr 15, 2005|
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