Application of Friedewald's LDL-cholesterol estimation formula to serum lipids in the Japanese population

When direct measurement of serum low density lipoprotein cholesterol (LDL-c) is not available, it can be estimated from total cholesterol (TC), triglycerides (TG) and high density lipoprotein cholesterol (HDL-c) by using the formula proposed by Friedewald: LDL-c = TC-[HDL-c + TG/k], k = 5 This formula assumes the triglyceride/cholesterol ratio in VLDL to be 5:1. However, it is changeable with serum triglyceride levels, and averaged as 4 among Japanese with triglycerides less than 400 mg/dl. The formula provides a better fit for Japanese people, when k = 4, rather than original k = 5. In addition, a better estimation is gained, if k is rotated according to the triglyceride levels of individual subjects; i.e. 3 for those with triglycerides less than 150 mg/dl, 4 for those with triglycerides from 150 to 299 mg/dl, 5 for those with triglycerides from 300 to 400 mg/dl. The percent error of estimation is less than 5% when k = 4, and about 1% when variable k is employed for populations of about 1,000 subjects in number.