Framingham Heart Study

The Framingham Heart Study (1,2) has published multivariate models for estimation of the 10-year absolute risk of developing coronary heart disease CHD (1).

• the Framingham Heart Study is an epidemiological study established in 1948 - 5,209 residents, 28 to 62 years old, of Framingham, Massachusetts, were recruited in a prospective epidemiologic cohort study. In 1971, an additional 5,124 subjects (offspring of original cohort subjects and spouses of offspring) were enrolled in the Framingham Offspring Study (3)
  • subjects have continued to return to the study every two years for a detailed medical history, physical examination, and laboratory tests.
  • factors age, gender, cigarette-smoking, blood cholesterol, high-density lipoprotein (HDL) cholesterol, blood pressure, left ventricular hypertrophy, and diabetes mellitus have been analysed in the Framingham Heart Study for the creation of a model for CHD prediction
    • calculation of Framingham risk score:
      • risk score was calculated for each subject using the risk score of Wilson et al (1)
        • subjects receive a point score based on categorical values of age, total cholesterol, high-density lipoprotein cholesterol, blood pressure, smoking, and diabetes. An online version of the calculator is available at http://hp2010.nhlbihin.net/atpiii/calculator.asp?usertype=prof
    • the Framingham risk score was designed to predict 10-year risk for CHD - subsequent analyses have shown that the Framlinghanm risk score is very effective in predicting the short-term cumulative risk for CHD, even in the context of competing risk of death from noncoronary causes
    • however there is study evidence that the Framingham 10-year risk model does not stratify lifetime risk of CHD effectively in some groups (4):
      • the Framingham risk score performed less well in stratifying lifetime risk younger men but improved at older ages as remaining life expectancy approached 10 years
        • note that it is likely that the composite Framingham risk score performed less well in predicting lifetime risk for CHD in younger subjects because of changes in risk factor status that occurred over time
          • rates of hypertension and diabetes increase sharply with age - this may alter the long-term risk of younger patients in an unpredictable fashion
        • Framingham risk score stratified lifetime risk well for women at all ages
        • the authors concluded that the Framingham 10-year CHD risk prediction model discriminated short-term risk well for men and women. However, it may not identify subjects with low short-term but high lifetime risk for CHD, likely due to changes in risk factor status over time

In addition to the limitations with respect to 10-year CHD and lifetime CHD risk as described, there are other potential limitations of the Framingham Heart study

• the risk estimating score sheets are only for persons without known heart disease
• the Framingham Heart Study risk algorithm encompasses only coronary heart disease, not other heart and vascular diseases
• the Framingham Heart Study population is almost all Caucasian. The Framingham risk algorithm may not fit other populations quite as well
• for some of the sex-age groups in Framingham, the numbers of events are quite small. Therefore, the estimates of risk for those groups may lack precision
• since age is a prominent determinant of the CHD risk score, the 10-year hazards of CHD are, on average, high in older persons. This may over-identify candidates for aggressive interventions. Relative risk estimates (risk in comparison with low risk individuals) may be more useful than absolute risk estimates in the elderly
• the Framingham subjects may have been motivated to modify risk factors (because of participation in periodic examinations) - this, in turn, could have decreased lifetime risk for CHD
• a study into the accuracy and impact of the use of the Framingham risk assessment revealed (5):
  • for CHD, the predicted to observed ratios ranged from an underprediction of 0.43 (95% CI 0.27 to 0.67) in a high-risk population to an overprediction of 2.87 (95% CI 1.91 to 4.31) in a lower-risk population
  • the study authors concluded that performance of the Framingham risk scores varies considerably between populations and evidence supporting the use of cardiovascular risk scores for primary prevention is scarce

Reference:

1. Wilson PW, D?Agostino RB, Levy D, Belanger AM, Silbershatz H, Kannel WB. Prediction of coronary heart disease using risk factor categories. Circulation 1998;97:1837?1847.
2. Dawber TR, Kannel WB, Lyell LP. An approach to longitudinal studies in a community: the Framingham study. Ann NY Acad Sci 1963;107:539?556.
3. Feinleib M, Kannel WB, Garrison RJ, McNamara PM, Castelli WP. The Framingham Offspring Study. Design and preliminary data. Prev Med 1975;4: 518?525.
4. Lloyd-Jones DM et al. Framingham Risk Score and Prediction of Lifetime Risk for Coronary Heart Disease.Am J Cardiol 2004;94:20?24
5. Brindle P et al. Accuracy and impact of risk assessment in the primary prevention of cardiovascular disease: a systematic review. Heart. 2006 Dec;92(12):1752-9