title: The measurement of 3-epimer 25-hydroxyvitamin D by mass spectrometry in clinical specimens detects inconsequential levels in adult subjects.
abstract: BACKGROUND
  Vitamin D is derived from dietary sources or from the action of ultraviolet light on 7-dehydrocholesterol and undergoes a number of enzymatic modifications that lead to the synthesis of active vitamin D metabolites or metabolites with reduced biological activity. Among these, epimerization at the 3-hydroxyl group leads to the synthesis of 3-epimer 25-hydroxyvitamin D (3EVD). Described first in biological system experiments using in vitro incubation of vitamin D in cell culture, this molecule has been reported as having distinct activities when compared with 25-hydroxy vitamin D (25OHVD). Measurements of vitamin D have been conducted using a variety of methodologies and have led to conflicting assessments of the quantities of 3EVD3 that are measured.
  
  
  METHODS
  The present article describes the development and use of a simple liquid chromatography-tandem mass spectrometry method validated by the Clinical Laboratory Improvement Amendments to quantitate 3EVD3 in 3528 subjects, including 309 children (162 are <2 years) and 232 pregnant women.
  
  
  RESULTS
  Our findings demonstrate that, although 3EVD3 constitutes a significant proportion of measureable 25OHVD3 in subjects younger than 1 year, 3EVD3 levels are negligible in most subjects older than 1 year.
  
  
  CONCLUSIONS
  It is important to choose the correct 25OHVD assay dependent on the age of the patient. Patients younger than 1 year should be run on a liquid chromatography-tandem mass spectrometry assay proven to not have potential contributions from any 3EVD present in the sample.
authors.affiliation: From the Quest Diagnostics Nichols Institute, San Juan Capistrano, CA.
authors.forename: Mildred M
authors.initials: MM
authors.lastname: Goldman
authors.forename: Khanh V
authors.initials: KV
authors.lastname: Viec
authors.forename: Michael P
authors.initials: MP
authors.lastname: Caulfield
authors.forename: Richard E
authors.initials: RE
authors.lastname: Reitz
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McPhaul
authors.forename: Nigel J
authors.initials: NJ
authors.lastname: Clarke
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001681:Biological Assay; D002112:Calcifediol / Q000097:blood; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007536:Isomerism; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D053719:Tandem Mass Spectrometry / Q000379:methods*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood / Q000737:chemistry; D055815:Young Adult
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D; D002112:Calcifediol