title: Serum level of fibroblast growth factor 23 in maintenance renal transplant patients.
abstract: BACKGROUND
  The discovery of fibroblast growth factor 23 (FGF23) provides a new conceptual framework that improves our understanding of the pathogenesis of post-transplant bone disease. Excess FGF23 is produced in the early post-transplant period; levels return to normal in the months following transplant. However, few manuscripts discuss FGF23 levels in stable long-term renal transplant recipients.
  
  
  METHODS
  We performed a cross-sectional observational study of 279 maintenance kidney recipients with chronic kidney disease (CKD) Stages 1-4 and stable allograft function who had received their transplant at least 12 months previously. We calculated the estimated GFR (eGFR) using the MDRD4 equation.
  
  
  RESULTS
  FGF23, parathyroid hormone (PTH) and phosphorus values were higher in more advanced stages, while the serum calcitriol levels and the phosphate reabsorption rate were lower. A significant inverse correlation was found between eGFR and FGF23 (r = -0.487; P < 0.001), PTH (r = -0.444; P < 0.001), serum phosphate levels (r = -0.315; P < 0.001) and fractional excretion of magnesium (r = -0.503; P < 0.001). Multivariable analysis showed that increased time on corticosteroids (P < 0.001), PTH (P < 0.001), serum phosphate (P = 0.003), decreased serum calcitriol (P = 0.049) and estimated glomerular filtration (P = 0.003) rate were associated with high FGF23 levels. In contrast with pre-transplant patients and first year post-transplant patients, higher FGF23 values were not correlated with increased phosphate excretion. An elevated phosphate reabsorption rate was associated with decreased PTH (P < 0.001) and calciuria (P = 0.028) and increased serum calcitriol (P = 0.009), plasma bicarbonate (P = 0.024) and estimated glomerular filtration (P = 0.003).
  
  
  CONCLUSIONS
  Serum FGF23 concentrations remain increased in long-term kidney graft recipients, even in the early stages of CKD. It remains to be seen whether measures aimed at reducing serum levels of PTH and phosphate and/or corticosteroid doses might help to lower serum FGF23 and whether this will improve kidney recipient outcomes.
authors.affiliation: Nephrology Department, Hospital Clínico Universitario San Carlos, Madrid, Spain. sanchezfructuoso@gmail.com
authors.forename: Ana I
authors.initials: AI
authors.lastname: Sánchez Fructuoso
authors.forename: Maria L
authors.initials: ML
authors.lastname: Maestro
authors.forename: Isabel
authors.initials: I
authors.lastname: Pérez-Flores
authors.forename: Rosalía
authors.initials: R
authors.lastname: Valero
authors.forename: Sara
authors.initials: S
authors.lastname: Rafael
authors.forename: Silvia
authors.initials: S
authors.lastname: Veganzones
authors.forename: Natividad
authors.initials: N
authors.lastname: Calvo
authors.forename: Virginia
authors.initials: V
authors.lastname: De la Orden
authors.forename: Jose C
authors.initials: JC
authors.lastname: De la Flor
authors.forename: Francisco
authors.initials: F
authors.lastname: Valga
authors.forename: Marta
authors.initials: M
authors.lastname: Vidaurreta
authors.forename: Cristina
authors.initials: C
authors.lastname: Fernández-Pérez
authors.forename: Alberto
authors.initials: A
authors.lastname: Barrientos
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D015519:Bone Density; D002117:Calcitriol / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000503:physiopathology*; D016030:Kidney Transplantation / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D010758:Phosphorus / Q000097:blood; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000601:surgery*
chemical_list: D015415:Biomarkers; C000717427:FGF23 protein, human; D010281:Parathyroid Hormone; D010758:Phosphorus; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D002117:Calcitriol