title: Free 25-Hydroxyvitamin D Concentrations in Cystic Fibrosis.
abstract: BACKGROUND
  Vitamin D deficiency is common in cystic fibrosis (CF), but there is no previous data on free 25-hydroxyvitamin D (25[OH]D) in CF or in relation to healthy individuals.
  
  
  METHODS
  We assessed total serum 25(OH)D concentration by chemiluminescence and serum free 25(OH)D concentration by both direct measurement (ELISA) and calculation, using serum albumin and vitamin D binding protein (VDBP) levels in 80 subjects (28 healthy adults, 25 clinically stable adults and children with CF and 27 adults experiencing a CF exacerbation).
  
  
  RESULTS
  Serum albumin and VDBP concentrations were lower in CF compared with healthy controls. Total serum 25(OH)D concentrations were positively correlated with both calculated and measured free 25(OH)D (P < 0.001 for both). Calculated and directly measured serum free 25(OH)D levels were positively correlated (P < 0.001).
  
  
  CONCLUSIONS
  Serum levels of directly measured free 25(OH)D positively correlated with total 25(OH)D, suggesting that achieving sufficient total serum 25(OH)D may result in adequate free 25(OH)D levels in CF.
authors.affiliation: Division of Endocrinology, Metabolism and Lipids (MJL, MDK, LH, TRZ, JAA, VT), Department of Medicine, Emory University, Atlanta, Georgia; Nutrition and Health Sciences Program (EMS, VT), Laney Graduate School, Emory University, Atlanta, Georgia; Atlanta Veterans Affairs Medical Center (VT), Section of Endocrinology, Atlanta, Georgia.
authors.forename: Moon Jeong
authors.initials: MJ
authors.lastname: Lee
authors.forename: Malcolm D
authors.initials: MD
authors.lastname: Kearns
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Smith
authors.forename: Li
authors.initials: L
authors.lastname: Hao
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Ziegler
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Alvarez
authors.forename: Vin
authors.initials: V
authors.lastname: Tangpricha
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D003550:Cystic Fibrosis / Q000097:blood / Q000188:drug therapy / Q000503:physiopathology; D061827:Dimensional Measurement Accuracy; D005260:Female; D005845:Georgia; D006801:Humans; D008297:Male; D017063:Outcome Assessment, Health Care; D062072:Patient Acuity; D012709:Serum Albumin / Q000032:analysis*; D013223:Statistics as Topic; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood / Q000627:therapeutic use*; D014809:Vitamin D-Binding Protein / Q000097:blood*; D014815:Vitamins / Q000627:therapeutic use
chemical_list: D012709:Serum Albumin; D014809:Vitamin D-Binding Protein; D014815:Vitamins; D014807:Vitamin D; C104450:25-hydroxyvitamin D