Analytical performance and clinical efficacy of three routine procedures for LDL cholesterol measurement compared with the ultracentrifugation-dextran sulfate-Mg2+ method

The diagnosis and management of adults with hypercholesterolemia in the US are largely based on low-density lipoprotein cholesterol (LDL-C) concentrat ion. In order to classify someone correctly into the National Cholesterol E ducation Program cut-points, LDL-C must be measured with a total error of l ess than or equal to 12%. We examined simultaneously the analytical and cli nical performance of two homogeneous LDL-C assays (LDL-C-RD, Roche Diagnost ics and LDL-C-GZ, Genzyme) and the Friedewald calculation (LDL-C-Fried). Th ese assays correlated highly with the ultracentrifugation-dextran sulfate-M g2+ method (LDL-C-RD: r = 0.962, y = 1.029x - 0.48 mmol/l, n = 134; LDL-C-G Z: r = 0.961, y = 0.986x - 0.12 mmol/l, n = 134; LDL-C-Fried: r = 0.960, y = 1.017x - 0.18 mmol/l, n = 115). The total error requirement was met by th e 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 compou nded imprecision of the three independent tests required for this calculati on 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 homogeneou s assays provide clinical laboratories with the means to measure LDL-C in h ypertriglyceridemic samples and could have a role in the diagnosis and mana gement of hyperlipidemic patients. (C) 2000 Elsevier Science B.V. All right s reserved.