Serum vitamin A and E analysis: comparison of methods between laboratories enrolled in an external quality assurance programme

Abstract

To survey laboratories enrolled in the Royal College of Pathologists of Australasia (RCPA) Chemical Pathology Quality Assurance Programme (QAP) for vitamin A and E testing to determine differences between methods of analysis. A detailed questionnaire covering the major aspects of serum vitamin A and E analysis was sent to all participating laboratories in 2007. Thirteen out of the 22 laboratories completed the questionnaire. Methods between laboratories showed a great deal of commonality. All respondents performed a liquid extraction step, which included the addition of an internal standard, followed by high-performance liquid chromatography (C18 columns with predominantly methanol-based mobile phases) with spectrophotometric detection. Major inter-laboratory differences were whether the sample was protected from light, the extraction solvents and ratios used, the drying down temperature used post-liquid extraction and choice of calibrator. The questionnaire highlighted discrete methodological differences between laboratories. These findings provide direction to enable the Vitamins Working Party of the Australasian Association of Clinical Biochemists to further investigate the dispersion in results between participants of the RCPA QAP vitamin programme.