COMPARISON OF HOSPITAL AND NEIGHBORHOOD CONTROLS IN A STUDY OF CORONARY-ARTERY DISEASE

Case-control studies of risk factors for coronary artery disease (CAD) have almost invariably employed hospital controls, with minimal or no coronary artery stenosis. Although there is an important advantage in knowing the CAD status of controls, such groups are subject to bias related to hospitalization. To evaluate the generalizability of results obtained from studies using hospital controls, we compared risk factors in 342 hospital controls free of angiographic evidence for CAD, 168 neighborhood controls without symptoms of CAD, and 450 CAD patients. Coronary artery disease in cases and hospital controls was established arteriographically. No significant differences were found between the male control groups for total and low density lipoprotein (LDL) cholesterol, LDL apo-B, pack-years of smoking, body mass index, proportion with hypertension, diabetes and family history of coronary heart disease. Compared with neighborhood controls, male hospital controls had significantly lower high density lipoprotein (HDL) cholesterol, higher triglycerides and uric acid and scored higher on the Framingham Type A behavior pattern scale. Among women, the hospital control group had significantly lower LDL cholesterol and fewer pack-years of smoking, and a greater prevalence of hypertension than the neighborhood group. A greater proportion of both male and female hospital controls had left ventricular hypertrophy, and there were more current smokers among the neighborhood controls in both sexes. Age adjustment did not change these comparisons. While very few neighborhood controls were treated with beta-blockers, 32.7% of male and 41.4% of female hospital controls were so medicated. Control for beta-blocker use eliminated the difference in HDL cholesterol and triglycerides between the two male control groups. For all variables, the differences between cases and the two control groups were always in the same direction. Thus, especially after controlling for the use of beta-blockers, most of the comparisons point to similarities rather than differences between the two control groups.