Validation and recalibration of the Framingham cardiovascular disease risk models in an Australian Indigenous cohort

Abstract

Background In Australia, clinical guidelines for primary prevention of cardiovascular disease recommend the use of the Framingham model to help identify those at high risk of developing the disease. However, this model has not been validated for the Indigenous population. Design Cohort study. Methods Framingham models were applied to the Well Person's Health Check (WPHC) cohort (followed 1998-2014), which included 1448 Aboriginal and Torres Strait Islanders from remote Indigenous communities in Far North Queensland. Cardiovascular disease risk predicted by the original and recalibrated Framingham models were compared with the observed risk in the WPHC cohort. Results The observed five- and 10-year cardiovascular disease probability of the WPHC cohort was 10.0% (95% confidence interval (CI): 8.5-11.7) and 18.7% (95% CI: 16.7-21.0), respectively. The Framingham models significantly underestimated the cardiovascular disease risk for this cohort by around one-third, with a five-year cardiovascular disease risk estimate of 6.8% (95% CI: 6.4-7.2) and 10-year risk estimates of 12.0% (95% CI: 11.4-12.6) and 14.2% (95% CI: 13.5-14.8). The original Framingham models showed good discrimination ability (C-statistic of 0.67) but a significant lack of calibration (χ² between 82.56 and 134.67). After recalibration the 2008 Framingham model corrected the underestimation and improved the calibration for five-year risk prediction (χ² of 18.48). Conclusions The original Framingham models significantly underestimate the absolute cardiovascular disease risk for this Australian Indigenous population. The recalibrated 2008 Framingham model shows good performance on predicting five-year cardiovascular disease risk in this population and was used to calculate the first risk chart based on empirical validation using long-term follow-up data from a remote Australian Indigenous population.

Keywords: Cardiovascular disease; Indigenous population; risk prediction; survival analysis.

Figure 1.

Calibration by decile for cardiovascular disease (CVD) risk of the original and recalibrated 2008 Framingham model. Horizontal-axes refer to decile of predicted risk based on the 2008 Framingham CVD model; vertical-axes refer to observed and model-based predicted probabilities of CVD event. (a) Original model (10-year risk), (b) Recalibrated model (five-year risk) and (c) Recalibrated model (10-year risk).

Figure 2.

Five-year cardiovascular risk charts based on the recalibrated Framingham model. This chart is based on 2008 Framingham model that has been recalibrated using information on Aboriginal and Torres Strait Islander participants from the Well Persons Health Check study, which recruited people from 26 remote communities from Far North Queensland. It has not been validated for use in other Indigenous populations. For people under treatment for high blood pressure, 5% should be added to the risk on the chart. HDL: high-density lipoprotein