Poor applicability of the Friedewald formula in the assessment of serum LDL cholesterol for clinical purposes

Objective: To determine the accuracy of the estimation of serum low-density lipoprotein (LDL) cholesterol concentration by the Friedewald formula. Methods: Modifications of the calculation formula are presented on the basis of ultracentrifugal separation of serum high-density lipoprotein and LDL cholesterol in the specimens collected (n = 1215) in a nationwide health survey. Results: The formulas obtained from different subject groups differed relatively little from each other. The accuracy of the original Friedewald formula was poor; in about 36% of the subjects the error was more than 5% compared with ultracentrifugally obtained results. By applying the currently recommended coronary heart disease (CHD) risk categorizations, high proportions (5%–28%) of the subjects were classified into wrong CHD risk categories when LDL cholesterol was calculated with any of the formulas. At high serum triglyceride levels, misclassifications were especially common. Conclusions: We conclude that even the most accurate LDL cholesterol calculation methods should be used with caution while classifying subjects into categories of CHD risk. In hypertriglyceridemic subjects, the calculation formulas probably should not be used at all.