Abstract

Objective: Serum low density lipoprotein (LDL) level is an important biomarker for coronary artery disease (CAD). As direct LDL measurement is expensive and not cost effective, especially in a large population, it is estimated by Friedewald formula. Therefore, we decided to compare the direct LDL measurement method with LDL measured by Friedewald formula in a large general population for the first time in Iran. Furthermore, we examined the association of total cholesterol (TCh), triglyceride (TG), and high density lipoprotein (HDL) with LDL. Subjects and Methods: This study was conducted on the subjects, aged 11-97 years, in the third phase of Isfahan Healthy Heart Program (IHHP) from three cities: Isfahan, Najafabad, and Arak. A fasting blood sample was taken from all subjects and referred to Isfahan Cardiovascular Research Center (ICRC) laboratory (central laboratory of IHHP) to assess TCh, TG, HDL, and LDL directly. Also, the LDL level was calculated by Friedewald formula, in addition. Results: The mean level of LDL by direct method was lower than that calculated by Friedewald formula. The mean difference between the two methods was significant, which was 6.6 +/- 15.5 mg/dl difference (t = -42.925, P < 0.0001). There was strong correlation between direct and calculated LDL levels (adjusted R-2 = 80.4). Using regression model, a new formula was found for the estimation of LDL. Conclusion: It is concluded that the Friedewald formula overestimates the LDL level compared to the direct method in general Iranian population. It is suggested that LDL measurement be carried out directly, especially in high-risk people. If a formula is necessary for LDL estimation, it is better to obtain an especial formula for each population.