ISSN 2149-2263 | E-ISSN 2149-2271
The Anatolian Journal of Cardiology
Analytical performance of a direct assay for LDL-cholesterol: a comparative assessment versus Friedewald’s formula [Anatol J Cardiol]
Anatol J Cardiol. 2005; 5(1): 13-17

Analytical performance of a direct assay for LDL-cholesterol: a comparative assessment versus Friedewald’s formula

Işık Türkalp1, Zafer Çil2, Didem Özkazanç3
1Diamed Dialysis Center, Laboratory of Biochemistry, Istanbul
2Karşıyaka State Hospital, Laboratory of Biochemistry, Izmir
3Haydarpaşa Numune Hospital, Laboratory of Biochemistry, Istanbul, Turkey

Objective: Because low density lipoprotein-cholesterol (LDL-C) is a modifiable risk factor for coronary artery disease (CAD), its routine measurement is recommended in the evaluation and management of hypercholesterolemia. Concentrations of LDL-C are commonly monitored by means of the Friedewald formula (FF), which provides a relative estimation of LDL-C concentration when the triglyceride (TGs) concentration is <200 mgr/dl and there are no abnormal lipids. Because of the limitations of the Friedewald calculation, direct methods for an accurate quantification of LDL-C are needed. Methods: We critically examined an immunoseparation method for direct assay of LDL-C in a comparison with FF. 1) We measured intraassay and interassay precision using quality-control sera and patient serum pools. Accuracy was evaluated from total error analyses. Sample stability was examined over 2 months. 2) The LDL-C levels obtained with direct assay were compared with those calculated by the FF in 47 randomly chosen patient samples. The samples were classified as group 1 (patients with TGs 60-308 mg/dl n=25) and group 2 (patients with TGs 320-695 mg/dl, n=22). Results: The direct immunoseparation assay displayed an excellent precision (total coefficient of variance (CV) <2.5%, intraassay CV<1.5% and interassay CV<1.5%). Mean total error was 4.34%. The direct assay met the current National Cholesterol Education Program (NCEP) requirements for LDL-C testing for precision and accuracy. The results of direct method (x) and the FF (y) were highly correlated (r=0.9908, y=1.030x-0.289, n=25) in group 1, but the results of two methods disagreed (r=0.716, y=0.956x-24.869, n=22) in group 2 (patients with TGs 320 -695 mg/dl). Conclusion: The direct immunoseparation assay meets the currently established analytical performance goals and may be useful for the diagnosis and management of hyperlipidemic patients.

Keywords: LDL--Cholesterol; direct assay; Friedewald formula; analytical performance

Işık Türkalp, Zafer Çil, Didem Özkazanç. Analytical performance of a direct assay for LDL-cholesterol: a comparative assessment versus Friedewald’s formula. Anatol J Cardiol. 2005; 5(1): 13-17
Manuscript Language: English


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