Performance of Calculated and Directly Measured Low-Density Lipoprotein Cholesterol in a Pediatric Population

An assessment of methods for the accurate measurement of low-density lipoprotein cholesterol (LDL-C) at decreased concentrations has not yet been carried out. We evaluated the performance of the Friedewald equation, a direct enzymatic assay, and a novel equation for determining LDL-C levels in a pediatric population with elevated triglycerides and reduced LDL-C levels.

LDL-C concentrations of 127 pediatric patients were determined by the Friedewald equation, a direct enzymatic assay, and a novel equation. The bias of each approach was assessed at selected LDL-C cutoffs and after stratifying samples by triglyceride content. The concordance of each approach, relative to the reference method, was determined at LDL-C cut-points of less than 70, 70 to 99, and 100 to 129 mg/dL.

The Friedewald equation substantially underestimated pediatric LDL-C concentrations below 100 mg/dL in the presence of elevated triglycerides. The Ortho Clinical Diagnostics (Raritan, NJ) direct LDL assay was positively biased at low LDL-C levels. The novel equation most effectively reduced the bias of the Friedewald equation at all LDL-C concentrations and increased the concordance of sample classification to the reference method.

The novel equation should be used for accurate measurement of pediatric LDL-C when the concentration is below 100 mg/dL in the presence of elevated triglycerides (150-399 mg/dL).