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CMAJ • November 14, 2000; 163 (10)
© 2000 Canadian Medical Association or its licensors

Research
Recherche

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

Steven A. Grover*, Marc Dorais*, Gilles Paradis{dagger}, J. George Fodor{ddagger}, Jiri J. Frohlich§, Ruth McPherson, Louis Coupal* and Hanna Zowall*

From *the Centre for the Analysis of Cost-Effective Care and the Divisions of General Internal Medicine and Clinical Epidemiology, The Montreal General Hospital, and the Departments of Medicine and Epidemiology and Biostatistics, McGill University; {dagger}the Division of Preventive Medicine, McGill University Health Centre and the Department of Epidemiology and Biostatistics, McGill University, Montreal, Que.; {ddagger}the Prevention and Rehabilitation Centre and ¶the Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ont.; and §the Healthy Heart Program, St. Paul's Hospital, Vancouver, BC.

Background: There is strong evidence to support the treatment of abnormal blood lipid levels among people with cardiovascular disease. Primary prevention is problematic because many individuals with lipid abnormalities may never actually develop cardiovascular disease. We evaluated the 1998 Canadian lipid guidelines to determine whether they accurately identify high-risk adults 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) were counted versus calculating risk using Framingham risk equations. We also compared the diagnostic accuracy of the 1998 guidelines with guidelines previously published by the National Cholesterol Education Program in the United States and the 1988 Canadian Consensus Conference on Cholesterol and then 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 risk factors for predicting CAD risk (areas under the ROC curves, 0.83 [standard deviation (SD) 0.02] v. 0.77 [SD 0.03], p < 0.05). Risk counting was a particularly poor method for predicting risk for women. The 1998 Canadian guidelines identified high-risk individuals more accurately than the earlier guidelines, but the increased accuracy was largely due to a lower false-positive rate or a higher true-negative rate (i.e., increased test specificity). Using the 1998 lipid guidelines we estimate that 5.9 million Canadians currently free of cardiovascular disease would be eligible for lipid screening and 322 705 (5.5%) would require therapy.

Interpretation: Calculating risk using risk equations is a more accurate method to identify people at high risk for CAD than counting the number of risk factors present, especially for women, and the 1998 Canadian lipid screening guidelines are significantly better at identifying high-risk patients than the 1988 guidelines. Many of our findings were incorporated into the new 2000 guidelines.




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