Validation of the Friedewald Equation for Evaluation of Plasma LDL-Cholesterol

In most clinical laboratories, low density lipoprotein (LDL) cholesterol is usually estimated indirectly with the Friedewald equation or directly with the N-geneous assay. We assessed LDL-cholesterol values obtained by both methods to find an appropriate fasting period and to assess the influence of the energy content of the last meal. Blood samples were taken from 28 healthy volunteers who had consumed a standard meal (107 g of carbohydrate, 658 kcal) followed by a fasting period of 12 and 18 h, or a high-energy meal (190 g of carbohydrate, 1011 kcal) with a fasting period of 12 h. Prolongation of the fasting period from 12 h to 18 h decreased glucose level, but did not decrease triacylglycerol, total cholesterol, or high density lipoprotein (HDL) cholesterol. LDL-cholesterol levels measured with the N-geneous assay did not change (94.0 +/- 21.5 to 96.3 +/- 19.1 mg/dl). LDL-cholesterol levels calculated with the Friedewald equation were also similar after fasting periods of 12 h (98.5 +/- 21.4 mg/dl) and 18 h (99.7 +/- 20.2 mg/dl). The high-energy meal did not change the level of LDL-cholesterol measured with the N-geneous assay (96.1 +/- 21.2 mg/dl), or the glucose, triacylglycerol, total cholesterol, or HDL-cholesterol level, but LDL-cholesterol levels evaluated from the Friedewald equation (92.6 +/- 20.3 mg/dl) became significantly lower. A fasting time longer than 12 h is not necessary to obtain reasonable blood lipid levels. The Friedewald equation gave higher LDL-cholesterol levels than N-geneous assay in young Japanese females who had eaten a low-energy meal, and lower values when they had eaten a high-energy meal. Thus, it may be necessary to pay attention to energy of nigh meal prior to blood withdrawal.