Gas chromatography—mass spectrometry and the measurement of vitamin D metabolites in human serum or plasma

Abstract

Although methods for the measurement of vitamin D metabolites continue to be developed, few have been properly validated by comparison with methods based on gas chromatography-mass spectrometry, widely accepted as being the definitive methodology. To the best of our knowledge, only three such comparisons have been carried out (14, 42, 83), all three examining HPLC assays for 25-OH-D. This lack of proper validation leads to lack of certainty as to the specificity of many assays widely used for clinical investigation. In our view there is an obvious need for the continuing development of mass fragmentographic assays for vitamin D and its metabolites, primarily for use as reference procedures for the evaluation of less rigorous methodologies. Provided standards, both labeled and unlabeled, become more widely available, development of specific mass fragmentographic assays for any metabolite of vitamin D should be possible. For metabolites where no specific binding protein or antiserum is available, mass fragmentography may be the only alternative.