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

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=1.029x-0.48 mmol/l, n=134; LDL-C(GZ): 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 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.