Effects of total cholesterol and triglyceride on the percentage difference between the low-density lipoprotein cholesterol concentration measured directly and calculated using the Friedewald formula.

Background: We elucidate how the triglyceride (TG) and total cholesterol (TC) concentrations affect the percentage difference (%DeltaLDL) between the low-density lipoprotein cholesterol (LDL-C) concentration evaluated by direct measurement (DLDL-C) and calculated using the Friedewald formula (FLDL-C), under conditions allowing the calculation.

Methods: Serum concentrations of TC, TG, high-density lipoprotein cholesterol (HDL-C), and DLDL-C were measured and the FLDL-C and %DeltaLDL were calculated for 38,243 Koreans who had TG values <4.52 mmol/L. The DLDL-C was measured using the homogeneous Kyowa Medex assay (Kyowa, Tokyo, Japan). The %DeltaLDL was calculated using the equation: [(FLDL-C-DLDL-C)/DLDL-C]x100.

Results: The mean %DeltaLDL-C was -9.1+/-6.4%. The %DeltaLDL differed by more than +/-5% in 75.4% of the subjects, and the FLDL-C was lower than the DLDL-C in 96.3%. The mean %DeltaLDL-C for the group with the highest TG and lowest TC was 11.8-fold that for the group with the lowest TG and highest TC.

Conclusions: Under conditions satisfying the requirements of the Friedewald formula, the DLDL-C and FLDL-C differed significantly over the concentration ranges of both TC and TG. In an evaluation of patients with hyperlipidemia, the Friedewald calculation may underestimate the risk for coronary heart disease.