Lipid screening to prevent coronary artery disease: a quantitative evaluation of evolving guidelines

Background: There is strong evidence to support the treatment of abnormal b lood lipid levels among people with cardiovascular disease. Primary prevent ion is problematic because many individuals with lipid abnormalities may ne ver actually develop cardiovascular disease. We evaluated the 1998 Canadian lipid guidelines to determine whether they accurately identify high-risk a dults for primary prevention. Methods: Using data from the Lipid Research Clinics and receiver operating characteristic (ROC) curves, we compared the diagnostic performance of the 1998 lipid guidelines when risk factors for coronary artery disease (CAD) w ere counted versus calculating risk using Framingham risk equations. We als o compared the diagnostic accuracy of the 1998 guidelines with guidelines p reviously published by the National Cholesterol Education Program in the Un ited States and the 1988 Canadian Consensus Conference on Cholesterol and t hen used Canadian Heart Health Survey data to forecast lipid screening and treatment rates for the Canadian population. Results: The Framingham risk equations were more accurate than counting ris k Factors for predicting CAD risk (areas under the ROC curves, 0.83 [standa rd deviation (SD) 0.02] v. 0.77 [SD 0.03], p < 0.05). Risk counting was a p articularly poor method for predicting risk for women. The 1998 Canadian gu idelines identified high-risk individuals more accurately than the earlier guidelines, but the increased accuracy was largely due to a lower false-pos itive rate or a higher true-negative rate (i.e., increased test specificity ). Using the 1998 lipid guidelines we estimate that 5.9 million Canadians c urrently free of cardiovascular disease would be eligible for lipid screeni ng and 322 705 (5.5%) would require therapy. Interpretation: Calculating risk using risk equations is a more accurate me thod to identify people at high risk for CAD than counting the number of ri sk factors present, especially for women, and the 1998 Canadian lipid scree ning guidelines are significantly better at identifying high-risk patients than the 1988 guidelines. Many of our findings were incorporated into the n ew 2000 guidelines.