Analytical performance and clinical efficacy of three routine procedures for LDL cholesterol measurement compared with the ultracentrifugation–dextran sulfate–Mg 2+ method

Abstract

The diagnosis and management of adults with hypercholesterolemia in the US are largely based on low-density lipoprotein cholesterol (LDL-C) concentration. In order to classify someone correctly into the National Cholesterol Education Program cut-points, LDL-C must be measured with a total error of ≤12%. We examined simultaneously the analytical and clinical performance of two homogeneous LDL-C assays (LDL-C RD, Roche Diagnostics and LDL-C GZ, Genzyme) and the Friedewald calculation (LDL-C Fried). These assays correlated highly with the ultracentrifugation–dextran sulfate–Mg 2+ method (LDL-C RD: r=0.962, y=1.029 x−0.48 mmol/l, n=134; LDL-C GZ: r=0.961, y=0.986 x−0.12 mmol/l, n=134; LDL-C Fried: r=0.960, y=1.017 x−0.18 mmol/l, n=115). The total error requirement was met by the LDL-C GZ assay at all clinical decision cut-points, whereas the LDL-C RD assay met this requirement only at LDL-C concentrations of 4.92 mmol/l. The LDL-C Fried failed to meet the total error requirement, because the compounded imprecision of the three independent tests required for this calculation was high. Both, the LDL-C GZ and the LDL-C RD assays appeared to be only slightly affected by increasing triglycerides. At the medical decision cut-point range, the LDL-C RD, LDL-C GZ and LDL-C Fried assays showed positive predictive values of 89–100, 85–100 and 83–99%, respectively, and negative predictive values of 52–98, 77–98 and 68–98%, respectively. The homogeneous assays provide clinical laboratories with the means to measure LDL-C in hypertriglyceridemic samples and could have a role in the diagnosis and management of hyperlipidemic patients.