Coronary risk assessment by point-based vs. equation-based Framingham models: significant implications for clinical care

Abstract

Background: US cholesterol guidelines use original and simplified versions of the Framingham model to estimate future coronary risk and thereby classify patients into risk groups with different treatment strategies. We sought to compare risk estimates and risk group classification generated by the original, complex Framingham model and the simplified, point-based version.

Methods: We assessed 2,543 subjects age 20-79 from the 2001-2006 National Health and Nutrition Examination Surveys (NHANES) for whom Adult Treatment Panel III (ATP-III) guidelines recommend formal risk stratification. For each subject, we calculated the 10-year risk of major coronary events using the original and point-based Framingham models, and then compared differences in these risk estimates and whether these differences would place subjects into different ATP-III risk groups (<10% risk, 10-20% risk, or >20% risk). Using standard procedures, all analyses were adjusted for survey weights, clustering, and stratification to make our results nationally representative.

Results: Among 39 million eligible adults, the original Framingham model categorized 71% of subjects as having "moderate" risk (<10% risk of a major coronary event in the next 10 years), 22% as having "moderately high" (10-20%) risk, and 7% as having "high" (>20%) risk. Estimates of coronary risk by the original and point-based models often differed substantially. The point-based system classified 15% of adults (5.7 million) into different risk groups than the original model, with 10% (3.9 million) misclassified into higher risk groups and 5% (1.8 million) into lower risk groups, for a net impact of classifying 2.1 million adults into higher risk groups. These risk group misclassifications would impact guideline-recommended drug treatment strategies for 25-46% of affected subjects. Patterns of misclassifications varied significantly by gender, age, and underlying CHD risk.

Conclusions: Compared to the original Framingham model, the point-based version misclassifies millions of Americans into risk groups for which guidelines recommend different treatment strategies.

Figure 1

Creation of analytic cohort and LDL treatment guidelines for patients undergoing Framingham-based risk stratification. *CHD risk equivalents included self-report of myocardial infarction, angina pectoris, diabetes mellitus, and stroke. †Persons taking lipid-lowering drugs ineligible for analysis. ‡CHD risk factors included: cigarette smoking, hypertension, HDL <40 mg/dl, family history of premature CHD, and age (>45 years for men, >55 years for women). Persons with HDL >60 mg/dl had 1 point subtracted from their risk factor sum score.

Figure 2

Classification of Subjects into Risk Groups by the Point-Based and Original Model. *Cells to the right of the diagonal represent the point-based system estimating a higher risk than the original model. Cells to the left of the diagonal represent the point-based system estimating a lower risk than the original model. Overall, 2,543 subjects contributed data toward this table

Figure 3

Classification of Subjects into Risk Groups by the Point-Based and Original Model. *Cells to the right of the diagonal represent the point-based system estimating a higher risk than the original model. Cells to the left of the diagonal represent the point-based system estimating a lower risk than the original model. Overall, 2,543 subjects contributed data toward this table