Phosphate metabolism and renal calcium stone disease

The purpose of the present investigation was to study various aspects of phosphate metabolism in renal calcium stone patients with special reference to the renal handling of phosphate and its relationship to other renal tubular functions and calcium metabolism. Serum phosphate and the capacity for renal tubular reabsorption of phosphate were lower in stone patients than in controls and decreased with advancing age. Reduced tubular phosphate reabsorption was particularly evident in stone patients with other tubular dysfunctions. Absorptive hypercalciuria was common, but unrelated to the renal tubular reabsorption of phosphate. Parathyroid hyperfunction was not observed in stone formers. Various loads of dietary phosphate resulted in similar renal adaptive responses in controls and stone formers. Orthophosphate supplementation had metabolic consequences with potentially beneficial effects for stone prevention (increased urinary pyrophosphate, decreased urinary calcium). The altered renal handling of phosphate in calcium stone formers may reflect a primary (independent of parathyroid hormone) renal tubular dysfunction in phosphate reabsorption.