title: Serum free 1,25-dihydroxy-vitamin D is more closely associated with fibroblast growth factor 23 than other vitamin D forms in chronic dialysis patients.
abstract: BACKGROUND
  Mineral bone disorder (MBD) is prevalent among chronic dialysis patients. However, relationship between different forms of vitamin D and fibroblast growth factor 23 (FGF-23) remains unclear in this population.
  
  
  METHODS
  A multicenter hemodialysis cohort was assembled. We evaluated 25-OH-D and 1,25-(OH)2-D, vitamin D-binding protein, and FGF-23, in this cohort. Multiple regression analyses were performed to investigate the relationship and stewardship between different vitamin D forms and FGF-23 concentrations.
  
  
  RESULTS
  Chronic dialysis patients presented significantly higher FGF-23 concentrations. 25-OH-D concentrations of <20 ng/ml (deficiency), 20-30 ng/ml (insufficiency), and ≥30 ng/ml (sufficiency) were associated with progressively lower FGF-23 concentrations (p<0.01). Serum FGF-23 concentrations were significantly correlated with total (p=0.02), free (p<0.01) and bioavailable (p<0.01) 25-OH-D and total (p=0.04), free (p=0.02), and bioavailable (p=0.03) 1,25-(OH)2-D concentrations. With all 25-OH-D and 1,25-(OH)2-D forms in the regression model, we found that free 1,25-(OH)2-D outweighed all other vitamin D forms regarding its association with FGF-23 (p=0.03).
  
  
  CONCLUSIONS
  The relationship between FGF-23 and vitamin D is stronger using free forms of 25-OH-D and 1,25-(OH)2-D. Subsequent studies aiming at MBD should consider including free 25-OH-D and 1,25-(OH)2-D in the analysis.
authors.affiliation: Division of Nephrology, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan; Department of Medicine, National Taiwan University Hospital, Jin-Shan branch, New Taipei City, Taiwan.
authors.forename: Chia-Ter
authors.initials: CT
authors.lastname: Chao
authors.affiliation: Division of Nephrology, Department of Internal Medicine, National Taiwan University Hospital, Yun-Lin branch, Yun-Lin County, Taiwan.
authors.forename: Szu-Ying
authors.initials: SY
authors.lastname: Lee
authors.affiliation: Division of Nephrology, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Chung-Jen
authors.initials: CJ
authors.lastname: Yen
authors.affiliation: Division of Nephrology, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Chih-Kang
authors.initials: CK
authors.lastname: Chiang
authors.affiliation: Division of Nephrology, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan. Electronic address: 007378@ntuh.gov.tw.
authors.forename: Jenq-Wen
authors.initials: JW
authors.lastname: Huang
authors.affiliation: Division of Nephrology, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Kuan-Yu
authors.initials: KY
authors.lastname: Hung
mesh_terms: D000368:Aged; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D006801:Humans; D008297:Male; D012044:Regression Analysis; D006435:Renal Dialysis; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood*
chemical_list: C000717427:FGF23 protein, human; D014807:Vitamin D; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23
keywords: End-stage renal disease; Fibroblast growth factor 23; Hemodialysis; Mineral bone disorder; Vitamin D