title: Fibroblast growth factor 23 is increased in calcium nephrolithiasis with hypophosphatemia and renal phosphate leak.
abstract: BACKGROUND
  Nephrolithiasis affects about 10% of the population in industrialized countries, with calcium salts composing more than 80% of renal stones. A significant percentage of patients with calcium nephrolithiasis and normal parathyroid function show hypophosphatemia and reduced renal phosphate reabsorption (i.e. a renal phosphate leak).
  
  
  OBJECTIVE
  The objective of the study was to compare serum levels of fibroblast growth factor 23 (FGF23), a regulator of phosphate homeostasis, in 110 recurrent stone formers with or without renal phosphate leak, six patients affected by X-linked hypophosphatemic rickets, five patients affected by oncogenic osteomalacia, and 60 unrelated healthy controls.
  
  
  METHODS
  This was a prospective interventional study.
  
  
  METHODS
  Renal phosphate leak was identified based on the occurrence of idiopathic hypophosphatemia [serum phosphate concentration < 2.50 mg/dl (<0.80 mmol/liter)] and reduced renal threshold phosphate concentration [<2.2 mg/liter (<0.70 mmol/liter)].
  
  
  RESULTS
  In 22 stone formers with renal phosphate leak, serum FGF23 concentration was significantly higher as compared with 88 stone formers without renal phosphate leak and with controls [83.3 (65.6-101.1) vs. 32.1 (26.8-37.4) and 24.5 (19.8-29.1) reference units (RU)/ml, respectively]. Stone formers with renal phosphate leak showed lower FGF23, compared with patients with oncogenic osteomalacia and X-linked hypophosphatemic rickets [572.3 (235.9-908.7) RU/ml]. Among stone formers and controls, serum FGF23 concentration displayed a strong inverse association with serum phosphate (r = -0.784, P = 0.009) and the rate of tubular phosphate reabsorption (r = -0.791, P = 0.008).
  
  
  CONCLUSIONS
  In our study population, renal phosphate leak affected 20% of stone formers and was strongly associated with increased serum FGF23 concentration.
authors.affiliation: Department of Clinical and Experimental Medicine, Università Federico II, Via S. Pansini, 5-80131 Naples, Italy.
authors.forename: Domenico
authors.initials: D
authors.lastname: Rendina
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Mossetti
authors.forename: Gianpaolo
authors.initials: G
authors.lastname: De Filippo
authors.forename: Michele
authors.initials: M
authors.lastname: Cioffi
authors.forename: Pasquale
authors.initials: P
authors.lastname: Strazzullo
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D015992:Body Mass Index; D002112:Calcifediol / Q000097:blood / Q000652:urine; D002117:Calcitriol / Q000097:blood / Q000652:urine; D002118:Calcium / Q000097:blood* / Q000652:urine; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood*; D006801:Humans; D017674:Hypophosphatemia / Q000097:blood* / Q000652:urine; D007669:Kidney Calculi / Q000097:blood* / Q000652:urine; D008297:Male; D010710:Phosphates / Q000097:blood / Q000652:urine; D011446:Prospective Studies; D012016:Reference Values
chemical_list: D015415:Biomarkers; C000717427:FGF23 protein, human; D010710:Phosphates; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium