Fibroblast Growth Factor 23 Is Increased in Calcium Nephrolithiasis with Hypophosphatemia and Renal Phosphate Leak

Context: 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). Objectives: 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. Design: 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 ( 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.