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Licensed Unlicensed Requires Authentication Published by De Gruyter December 22, 2008

Freeze-thaw and matrix effects in direct high-density lipoprotein cholesterol methods

  • Christa Cobbaert , Corrie van Haperen , Claudia Bastijns and Pierre N.M. Demacker


Background: There is frequent discussion on the susceptibility of direct high-density lipoprotein cholesterol (HDL-C) methods to matrix effects. In Vitro Diagnostics manufacturers recognize this issue and regularly improve their HDL-C reagent formulations in subsequent generations.

Methods: The 3rd generation direct HDL-C assay from Roche was investigated for matrix effects in comparison to the former generation, a Beckman direct HDL-C method and a conventional phosphotungstate (PTA)/Mg2+ precipitation method. In addition, 235 heparin plasma samples were measured freshly and after a freeze-thaw cycle with the Roche 2nd and 3rd generation direct HDL-C. Biases, outliers, and intraclass correlation coefficients (ICCs) were calculated for both experiments. Multivariate analysis was used to investigate interference by matrix components.

Results: In fresh samples, Roche 2nd and 3rd generation HDL-C methods averaged +0.15 mmol/L (95% CI: 0.13–0.16) and +0.08 mmol/L (95% CI: 0.07–0.09) higher compared to frozen samples. In frozen aliquots, ICCs for Roche 2nd and 3rd generation and Beckman direct HDL-C as compared to PTA/MgCl2 were 0.963, 0.966, and 0.924, respectively. Predictors of outliers (defined as having an absolute difference >0.21 mmol/L) in comparisons of direct methods to the PTA/MgCl2 precipitation method were high triglyceride and low albumin levels.

Conclusions: The 3rd generation direct HDL-C from Roche has become insensitive to most matrix effects, bringing along more accurate results in hypoalbuminemic and hypertriglyceridemic samples. Surprisingly, Roche direct assays produced significantly higher HDL-C levels in fresh samples compared to frozen plasma samples. If confirmed by others, the latter finding has implications for patient management and necessitates further reagent optimization.

Clin Chem Lab Med 2009;47:172–6.

Corresponding author: C. Cobbaert, PhD, Department of Clinical Chemistry and Hematology, Amphia Hospital, Molengracht 21, 4880 Breda, The Netherlands

Received: 2008-8-4
Accepted: 2008-11-3
Published Online: 2008-12-22
Published in Print: 2009-02-01

©2009 by Walter de Gruyter Berlin New York

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