Role of the apolipoprotein B-apolipoprotein A-I ratio in cardiovascular risk assessment: a case-control analysis in EPIC-Norfolk.

ABSTRACT

BACKGROUND: An elevated apolipoprotein B-apolipoprotein A-I (apo B-apo A-I) ratio is a risk factor for future coronary artery disease (CAD). It is not known whether this ratio is better than traditional lipid values for risk assessment and prediction and whether it adds predictive value to the Framingham risk score. OBJECTIVE: To evaluate whether the apo B-apo A-I ratio is associated with future CAD events independent of traditional lipid measurements and the Framingham risk score and to evaluate the ability of this ratio to predict occurrence of future CAD. DESIGN: Prospective, nested case-control study. SETTING: Norfolk, United Kingdom. PARTICIPANTS: Apparently healthy men and women (45 to 79 years of age) in the European Prospective Investigation into Cancer and Nutrition-Norfolk. Cases (n = 869) were persons who developed fatal or nonfatal CAD. Controls (n = 1511) were persons without CAD who were matched for age, sex, and enrollment period. MEASUREMENTS Total cholesterol, high-density lipoprotein (HDL) cholesterol, triglyceride, apolipoprotein, and C-reactive protein levels were measured directly. Low-density lipoprotein (LDL) cholesterol values were calculated by using the Friedewald formula. RESULTS: The apo B-apo A-I ratio was associated with future CAD events, independent of traditional lipid values (adjusted odds ratio, 1.85 [95% CI, 1.15 to 2.98]), including the total cholesterol-HDL cholesterol ratio, and independent of the Framingham risk score (adjusted odds ratio, 1.77 [CI, 1.31 to 2.39]). However, it did no better than lipid values at discriminating between CAD cases and controls (area under the receiver-operating characteristic curve, 0.670 for total cholesterol-HDL cholesterol ratio vs. 0.673 for apo B-apo A-I ratio [P = 0.38]) and added little to the predictive value of the Framingham risk score (area under the receiver-operating characteristic curve, 0.594 for Framingham risk score alone vs. 0.613 for Framingham risk score plus apo B-apo A-I ratio [P < 0.001]). In addition, it incorrectly classified 41.1% of cases and 50.4% of controls. LIMITATIONS: No participant was taking lipid-lowering medication, and diabetes was uncommon. CONCLUSIONS: The apo B-apo A-I ratio is independently associated with, but adds little to, existing measures for CAD risk assessment and discrimination in the general population. Other characteristics of the test, such as the ability to perform it on nonfasting samples, may still make it useful in some settings.