BACKGROUND: The Joint British Societies Coronary Risk Prediction Charts recommend the use of a high-density lipoprotein cholesterol value of 1 mmol/l where actual values have not been measured. It is important to quantify the impact of this advice if risk assessments are to be sufficiently accurate to guide treatment decisions. DESIGN: The risks of 5005 individuals from the Health Survey for England 1998 were calculated using the Joint British Societies charts. Each individual's risk was recalculated assuming a high-density lipoprotein cholesterol value of 1 mmol/l. These risk estimates were compared with those derived from the Framingham equation. METHODS: Using the Framingham equation as the gold standard, the positive and negative predictive values, sensitivity and specificity with 95% confidence intervals of the Joint British charts with actual and estimated high-density lipoprotein cholesterol values were calculated. RESULTS: At the 30% 10-year coronary heart disease risk threshold using measured high-density lipoprotein cholesterol values, the charts had a sensitivity of 83% and specificity of 99%. Using an estimated high-density lipoprotein cholesterol value of 1 mmol/l reduced the sensitivity to 58% with a specificity of 98%. CONCLUSIONS: In the presence of measured high-density lipoprotein cholesterol values there was good agreement between the Framingham equation and the Joint British Societies charts. The use of a fixed high-density lipoprotein cholesterol value of 1 mmol/l introduced important and significant errors into the risk assessment. This study reinforces the need to measure both total and high-density lipoprotein cholesterol when assessing coronary risk.
BACKGROUND: The Joint British Societies Coronary Risk Prediction Charts recommend the use of a high-density lipoprotein cholesterol value of 1 mmol/l where actual values have not been measured. It is important to quantify the impact of this advice if risk assessments are to be sufficiently accurate to guide treatment decisions. DESIGN: The risks of 5005 individuals from the Health Survey for England 1998 were calculated using the Joint British Societies charts. Each individual's risk was recalculated assuming a high-density lipoprotein cholesterol value of 1 mmol/l. These risk estimates were compared with those derived from the Framingham equation. METHODS: Using the Framingham equation as the gold standard, the positive and negative predictive values, sensitivity and specificity with 95% confidence intervals of the Joint British charts with actual and estimated high-density lipoprotein cholesterol values were calculated. RESULTS: At the 30% 10-year coronary heart disease risk threshold using measured high-density lipoprotein cholesterol values, the charts had a sensitivity of 83% and specificity of 99%. Using an estimated high-density lipoprotein cholesterol value of 1 mmol/l reduced the sensitivity to 58% with a specificity of 98%. CONCLUSIONS: In the presence of measured high-density lipoprotein cholesterol values there was good agreement between the Framingham equation and the Joint British Societies charts. The use of a fixed high-density lipoprotein cholesterol value of 1 mmol/l introduced important and significant errors into the risk assessment. This study reinforces the need to measure both total and high-density lipoprotein cholesterol when assessing coronary risk.