A modified formula for calculating low-density lipoprotein cholesterol values

Background: The Friedewald formula (FF) is useful for calculating serum low-density lipoprotein cholesterol (LDL-C) values, but has a remarkable deviation and limitation especially in hypertriglyceridemia. We modify the formula which is now more suitable for LDL-C calculation. Methods: 2180 cases were classified into three groups according to their TG concentrations (A: < 200 mg/dl, n = 1220; B: 200-400 mg/dl, n = 480; C: 400-1000 mg/dl, n = 480). The concentrations of LDL-C were measured or estimated by 1) a direct measurement (DM); 2) the FF; and 3) our modified Friedewald formula (MFF): LDL-C (mg/dl) = Non-HDL-C x 90% - TG x 10%. Results: Linear regression showed a significant correlation (P < 0.001) between the measured and calculated LDL-C values. Bland-Altman plots indicated that the methods (DM/MFF) were in better agreement than those (DM/FF). The LDL-C/Non-HDL-C ratio in FF calculated values was significantly lower (P < 0.05) than that in MFF or DM values, while no significant difference between MFF and DM was found. In Group A and Group B, 4.26% and 14.79% of the MFF calculated values had more than 20% deviation from those measured by DM. These percentages were significantly lower than those calculated by FF, where 7.30% and 25.63% were observed, respectively (P < 0.01 and P < 0.001). The MFF calculated values were all positive even in Group C. Conclusions: Compared with the FF calculation, serum LDL-C values estimated by our modified formula are closer to those measured by a direct assay. The modification significantly diminishes the interference caused by hypertriglyceridemia.