Study: Simplified Framingham risk score could misclassify millions

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Use of the conventional simplified version of the Framingham risk score model may underestimate the risk of cardiovascular (CV) events in millions of Americans, according to a study published online Sept. 8 in the Journal of General Internal Medicine.

The original Framingham model estimates risk based on a patient's age, total and HDL cholesterol, systolic blood pressure, treatment for hypertension and smoking status. Because it is a complex formula that needs to be determined with a calculator or computer, it has been simplified into a point-based system that assigns each risk factor level a number. These risk factor values are then added up into a score; the risk for that score is then determined from a table.

Today's computers or PDAs, however, can easily calculate the once-complex formula, according to the authors.

To understand the effectiveness of Framingham risk score models, William J. Gordon, MD, of Weill Cornell Medical College in New York City, and colleagues from San Francisco VA Medical Center and the University of California, San Francisco compared the differences between the two models to predict cardiac risk.

The researchers used National Health and Nutrition Examinations Survey responses conducted by the Centers for Disease Control and Prevention between 2001 and 2006 to assess 2,543 patients, who would represent the 39 million people that were recommended to undergo Framingham risk score screening to predict CV risk.

Results showed that 15 percent of the patients under the point-based system were classified as being at a different risk level then they were when the original Framingham risk score system was utilized. According to the authors, this could mean that 5.7 million Americans would have had miscalculated risk scores.

Additionally, the researchers estimated that 3.9 million were misclassified into higher risk groups, while 1.8 million were misclassified as being lower risk.

“Across the group, on average, these statistical differences balance out," said senior author Michael Steinman, MD. "But for individual patients, they are potentially important. A lot of individuals would be treated differently—either more aggressively or less aggressively—using the point-based model."

Researchers said the simplified point-based system is completed with pen and paper and was introduced almost a decade ago, before computers and other technology came of age.

"While the point-based system is a substantial improvement over having no standardized method for predicting risk, just about any computer or PDA [personal digital assistant] in use today can calculate the original Framingham model," said Steinman. "This means that your doctor can calculate your risk just as easily using the complex equation, which is likely to be more accurate than the point-based system. So there's not much reason to use the point-based system anymore in most instances.

"With risk prediction models being increasingly used for many different diseases and conditions, this could be a general problem in the field of medicine," Steinman concluded. "In creating simplified risk models, we have to be aware of the potential impact on individual patients."

The study was funded by the National Institute on Aging, the American Federation for Aging Research, the Hartford Foundation, the Department of Veterans Affairs and the National Institutes of Health.