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Eva M.L. Smets, Nathalie C.V. Péquériaux, Victor Blaton, Henk M.J. Goldschmidt

Analytical Performance of a Direct Assay for LDL-Cholesterol

We evaluated a direct assay for the determination of LDL-cholesterol (LDL-C) L-Type assay, Wako Pure Chemicals in two laboratories. This assay is applicable to most random access clinical chemistry analyzers, allowing full automation.

Between-run coefficient of variation (NCCLS EP5) varied between 1.29 ? and 3.13 ? and thus met the National Cholesterol Education Program (NCEP) goal. The assay was considered linear over a physiologically relevant range of LDL-C, 2.22 to 7.04 mmol/l (NCCLS EP6).

Method comparison yielded identical results at both evaluation sites for LDL-C when assayed with the direct method. LDL-C results obtained with the homogeneous method under investigation (y) differed significantly from values from density-gradient ultracentrifugation (x) according to Chung (y = 0.87x + 0.43 mmol/l, s_yx = 0.38 mmol/l, r = 0.91). With the latter method as a reference method, mean bias was 3.16 ? meeting the NCEP criteria. Diagnostic performance was excellent at a clinically relevant cut-off level of 3.37 mmol/l. Results of the direct method (y) and the commonly used Friedewald formula (x) were highly correlated (s_yx = 0.22 mmol/l, r = 0.97), but both slope and intercept differed significantly from one and zero respectively (y = 0.90x + 0.37 mmol/l).

Bilirubin, hemolysis and ascorbate did not interfere; triglycerides did not cause clinically relevant interference below 11.3 mmol/l.

The direct method we investigated is user-friendly and provides an improvement in the determination of LDL-C in routine laboratories.

Clinical Chemical Laboratory Medicine, Walter de Gruyter

Print ISSN: 1434-6621
Volume: 39, 04/2001
Pages: 270 - 280

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