| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1968667 | Clinical Biochemistry | 2013 | 5 Pages |
•Three vitamin E calibrators were compared by LC–tandem mass spectrometry methods.•Discordance between the calibrators is greater than the assay uncertainty.•Lack of agreement between calibrators is an obstacle to result harmonization.
ObjectivesAlpha-tocopherol is the predominant form of vitamin E in plasma and is routinely measured to assess vitamin E status. Agreement between vitamin E assays is essential to provide consistent result interpretation. Lack of agreement among calibrators is potentially a significant obstacle to method harmonization. The aim of this study was to ascertain the agreement between commercial secondary calibrators for analysis of serum/plasma alpha-tocopherol using two methods of isotope dilution liquid chromatography–tandem mass spectrometry (LC–MSMS).Design and methodsThree commercial single level calibrators (Bio-Rad Laboratories, Chromsystems Diagnostics and RECIPE) were prepared in quintuplicate in conjunction with an in-house calibrator set for alpha-tocopherol. Samples were analyzed by two methods using an Agilent-6490 LC–MSMS.ResultsThe linearity of both methods ranged from at least 4 to 70 μmol/L. The expanded within run imprecision of both LC–MSMS methods was ± 6% at 95.4% confidence interval across the assay range. The percentage observed difference for the commercial calibrators was calculated from the observed mean against the given value of the calibrator: Bio-Rad (bias + 1.4% in both methods); Chromsystems (bias + 5.4% [first method] and + 5.0% [second method]); and RECIPE (bias − 8.9% [first method] and − 9.8% [second method]).ConclusionsResults demonstrate an overall discordance between the commercial calibrators that is greater than the assay uncertainty. It is observed that the greatest deviation of the three calibrators is traceable to a different standard reference material. This lack of harmonization means that results from different laboratories may not be comparable.
