title: Mass spectrometric profiling of vitamin D metabolites beyond 25-hydroxyvitamin D.
abstract: BACKGROUND
  The frequency of measurements of vitamin D in the human population has significantly increased over the last decade because vitamin D has now been linked to many diseases, in addition to its established role in bone health. Usually, serum 25-hydroxyvitamin D concentrations are measured to assess the vitamin D status of individuals. Unfortunately, many studies investigating links between vitamin D and disease also use only this single metabolite. Intricate correlations with other vitamin D metabolites or dynamic effects of downstream metabolites may therefore be overlooked. Fortunately, powerful LC-MS/MS approaches have recently become available that can simultaneously quantify the concentrations of multiple vitamin D metabolites. These approaches are challenging, however, because of inherent instrumental problems with detection of vitamin D compounds and the low concentrations of the metabolites in biological fluids.
  
  
  BACKGROUND
  This review summarizes recent mass spectrometry assays for the quantitative measurement of multiple vitamin D metabolites and their application in clinical research, with a particular focus on the low-abundance downstream metabolic species generated after the initial hydroxylation to 25-hydroxyvitamin D.
  
  
  CONCLUSIONS
  To study the pathobiological effects and function of vitamin D metabolites in disease, in particular in low-abundance species beyond 25-hydroxyvitamin D, we need to know their concentrations. Although detection of these vitamin D species is challenging, a number of recent mass spectrometry assays have successfully demonstrated that LC-MS/MS methods can quantify multiple vitamin D compounds over a wide dynamic range individually or as part of multimetabolite assays.
authors.affiliation: Institute of Bioanalytical Chemistry, Saarland University, Saarbrücken, Germany.
authors.forename: Miriam J
authors.initials: MJ
authors.lastname: Müller
authors.affiliation: Institute of Bioanalytical Chemistry, Saarland University, Saarbrücken, Germany. dietrich.volmer@mx.uni-saarland.de.
authors.forename: Dietrich A
authors.initials: DA
authors.lastname: Volmer
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods*; D055432:Metabolomics; D053719:Tandem Mass Spectrometry / Q000379:methods; D014807:Vitamin D / Q000031:analogs & derivatives / Q000032:analysis* / Q000097:blood / Q000378:metabolism*
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D