LDL cholesterol calculation methods and their influence on the indications for cholesterol-lowering treatment.

INTRODUCTION The Friedewald equation is problematic at high triglyceride or low LDL-c levels. Alternatives, such as the Martin-Hopkins or Sampson-NIH equations, have been proposed. This study aims to compare LDL-c estimates derived from these 3 equations with directly measured LDL-c and to assess whether the choice of equation affects clinical management.

METHODS  LDL-c levels calculated on the 3 equations were compared with measured LDL values. Comparisons were stratified by total triglyceride (TG) (0-400 mg/dL, 400-800 mg/dL and >800 mg/dL) and LDL-c levels (below or above 70 mg/dL). Random samples were selected from each category (TG 0-400 mg/dL, TG 400-800 mg/dL and LDL-c <70 mg/dL) and the misclassification rates attributable to each equation were determined in subjects in secondary prevention.

RESULTS  In subjects with TG 0-400 mg/dL, the misclassification rate was 4.4% on Sampson-NIH, 4.9% on Martin-Hopkins and 6.4% on Friedewald. In subjects with TG 400-800 mg/dL, rates were 7.4%, 3.7% and 14.8%, respectively. In subjects with LDL-c <70mg/dL, rates were 14.7%, 14.7% and 17.6%, respectively.

CONCLUSION  This study demonstrated that the 3 methods performed very well in subjects with TG 0-400 mg/dl, relatively well for TG 400-800 mg/dL and less well for LDL-c <70 mg/dL. However, the Sampson and Martin-Hopkins equations were less prone to therapeutic misclassification errors than the Friedewald equation.