title: Role of fibroblast growth factor 23 (FGF23) in the metabolism of phosphorus and calcium immediately after kidney transplantation.
abstract: BACKGROUND
  Persistence of inappropriately high serum levels of fibroblast growth factor-23 (FGF23), a recently discovered phosphaturic hormone, has been reported to play an important role in the pathogenesis of posttransplant hypophosphatemia. The aim of the present study was to evaluate FGF23 in the early posttransplant period and study the complex associations between FGF23, parathyroid hormone (PTH), 1,25(OH)(2) vitamin D, and phosphate in transplant patients.
  
  
  METHODS
  We performed a cross-sectional observational study of 42 adult kidney recipients in the early posttransplant period (<6 months). Fasting serum samples and 24-hour urine samples were collected during a routine follow-up outpatient visit. Serum creatinine, calcium, phosphate, magnesium and urinary creatinine, calcium, magnesium, and phosphate were measured using standard assays. We also studied concentrations of 25 hydroxyvitamin D, 1,25(OH)(2) vitamin D, intact PTH, and circulating FGF23.
  
  
  RESULTS
  Median values for the different parameters studied were as follows: 9.9 ± 0.6 mg/dL, phosphatemia 3.3 ± 0.7 mg/dL, estimated glomerular filtration rate (eGFR; 41.1 ± 14.0 mL/min, phosphate reabsorption rate 68.4% ± 10.7%, PTH 94.5 ng/L (53.8-199.5), calcitriol 33.0 pg/mL (24.0-44.1), calcidiol 27.3 ng/mL (17.0-38.0), FGF23 139 pg/mL (88-221), and calciuria 62.5 mg/d (40.3-101.3). The variables significantly associated with serum FGF23 levels were phosphate reabsorption rate (r = .493; P = .001), calcitriol (r = .399; P = .009), eGFR (r = .557; P < .001), PTH (0.349; P = .024).
  
  
  CONCLUSIONS
  Elevated serum levels of FGF23 could explain the deficiency of calcitriol and elevated renal phosphorus wasting in the early posttransplant period. All treatments that can lead to increased serum phosphate levels (eg, oral medication or calcitriol) should be carefully evaluated, since increased phosphatemia could further stimulate secretion of FGF23 and prolong high phosphorus loss.
authors.affiliation: Nephrology Department, Hospital Clinico San Carlos, Madrid, Spain. sanchezfructuoso@gmail.com
authors.forename: A I
authors.initials: AI
authors.lastname: Sánchez Fructuoso
authors.forename: M L
authors.initials: ML
authors.lastname: Maestro
authors.forename: N
authors.initials: N
authors.lastname: Calvo
authors.forename: V
authors.initials: V
authors.lastname: De La Orden
authors.forename: I
authors.initials: I
authors.lastname: Pérez Flores
authors.forename: M
authors.initials: M
authors.lastname: Vidaurreta
authors.forename: R
authors.initials: R
authors.lastname: Valero
authors.forename: C
authors.initials: C
authors.lastname: Fernández-Pérez
authors.forename: A
authors.initials: A
authors.lastname: Barrientos
mesh_terms: D015415:Biomarkers / Q000097:blood / Q000652:urine; D002118:Calcium / Q000097:blood* / Q000652:urine; D016009:Chi-Square Distribution; D003430:Cross-Sectional Studies; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D005919:Glomerular Filtration Rate; D006801:Humans; D017674:Hypophosphatemia / Q000097:blood / Q000209:etiology* / Q000503:physiopathology / Q000628:therapy / Q000652:urine; D016030:Kidney Transplantation / Q000009:adverse effects*; D010281:Parathyroid Hormone / Q000097:blood; D010758:Phosphorus / Q000097:blood* / Q000652:urine; D013997:Time Factors; D015854:Up-Regulation; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood
chemical_list: D015415:Biomarkers; C000717427:FGF23 protein, human; C470125:PTH protein, human; D010281:Parathyroid Hormone; D014807:Vitamin D; D010758:Phosphorus; D005346:Fibroblast Growth Factors; C097949:1,25-dihydroxyvitamin D; D000089703:Fibroblast Growth Factor-23; D002118:Calcium