title: 25-Hydroxyvitamin D C3-epimer is universally present in neonatal Western Australian samples but is unlikely to contribute to diagnostic misclassification.
abstract: BACKGROUND
  The presence of C3-epimer (C-3-epi-25-hydroxyvitamin D) in infant serum may complicate 25-hydroxyvitamin D (25(OH)D) measurement when using liquid chromatography tandem mass spectrometry assays that do not separately measure the epimer. We measured the concentration of C3-epi-25(OH)D in neonatal samples in Western Australian using umbilical cord blood samples and a liquid chromatography tandem mass spectrometry assay that separately quantifies 25(OH)D and C3-epi-25(OH)D.
  
  
  METHODS
  A total of 120 anonymized cord blood samples were analysed using a liquid chromatography tandem mass spectrometry assay that utilizes two CSH fluoro-phenyl columns in series. Chromatography was performed on a Waters Acquity Ultra Performance Liquid system, and quantification was using a Waters Quattro Premier XE mass spectrometer.
  
  
  RESULTS
  C3-epi-25(OH)D3 was detected in all umbilical cord blood samples (median 5.2 nmol/L, IQR 3.7-6.6 nmol/L) and contributed 6.6% (SD 2.6, 95% CI [6.1, 7.1]) of the total 25(OH)D concentration. Mean 25(OH)D3 measured in cord blood was 79.1 nmol/L (SD 22.7 nmol/L). A positive relationship (R(2 )= 0.35, P < 0.0005) between 25(OH)D3 levels and C3-epi-25(OH)D3 was noted in this cohort. No samples contained 25(OH)D2 or C3-epi-25(OH)D2.
  
  
  CONCLUSIONS
  C3-epi-25(OH)D3 is present in all neonatal samples but contributes <10% of the total 25(OH)D concentration which is unlikely to be clinically significant. Liquid chromatography tandem mass spectrometry assays that do not separately quantify C3-epi-25(OH)D3 from other vitamin D metabolites may potentially overestimate neonatal 25(OH)D levels, but diagnostic misclassification in neonates is unlikely.
authors.affiliation: School of Medicine and Pharmacology, University of Western Australia, Perth, Western Australia, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Cooke
authors.affiliation: Department of Clinical Biochemistry, Pathwest Royal Perth Hospital, Perth, Western Australia, Australia.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Cooke
authors.affiliation: School of Medicine and Pharmacology, University of Western Australia, Perth, Western Australia, Australia Department of Clinical Biochemistry, Pathwest Royal Perth Hospital, Perth, Western Australia, Australia Clinical Biochemistry, St John of God Pathology, Western Australia, Australia.
authors.forename: Damon A
authors.initials: DA
authors.lastname: Bell
authors.affiliation: Department of Clinical Biochemistry, Pathwest Royal Perth Hospital, Perth, Western Australia, Australia School of Pathology and Laboratory Medicine, University of Western Australia, Perth, Western Australia, Australia.
authors.forename: Samuel D
authors.initials: SD
authors.lastname: Vasikaran
authors.affiliation: School of Medicine and Pharmacology, University of Western Australia, Perth, Western Australia, Australia Department of Clinical Biochemistry, Pathwest Royal Perth Hospital, Perth, Western Australia, Australia Paul.Glendenning@health.wa.gov.au.
authors.forename: Paul
authors.initials: P
authors.lastname: Glendenning
mesh_terms: D005312:Fetal Blood; D006801:Humans; D007231:Infant, Newborn; D059629:Signal-To-Noise Ratio; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014904:Western Australia
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: C3-epimer; LC-MS/MS; Vitamin D; cord blood; mass spectrometry