Estimating low-density lipoprotein cholesterol by the Friedewald equation is adequate for classifying patients on the basis of nationally recommended cutpoints

Abstract

We compared low-density lipoprotein cholesterol (LDL) values obtained by the Friedewald formula - i.e., total cholesterol minus high-density lipoprotein (HDL) cholesterol minus very-low-density lipoprotein (VLDL) cholesterol (estimated as triglyceride ÷ 5) - with those obtained by lipoprotein fractionation, using 4736 specimens. When triglycerides were <2.0 g/L, >90% of estimated LDL cholesterol values were acceptable, within ±10% of measured values. At triglyceride concentrations of 2.0-4.0 g/L and 4.0-6.0 g/L, only 72% and 39%, respectively, of the estimates were acceptable. LDL values derived from an alternative formula, estimating VLDL as triglycerides ÷ 6, were even less accurate. Nevertheless, the use of estimated LDL for risk classification based on the National Cholesterol Education Program Adult Treatment Panel cutpoints of 1.30 and 1.60 g/L was considered acceptable. At triglyceride concentrations ≤5.0 g/L, 88% of classifications based on estimated LDL (using triglycerides ÷ 5) were concordant with those by measured LDL. Eleven percent of classifications were shifted across one outpoint, evenly distributed between high and low. Fewer than 1% of classifications, all with Type III hyperlipoproteinemia, were misclassified two cutpoints high. Refinements in the estimation model did not substantially improve LDL estimation or concordance of risk classification.