[Clinical aspect of recent progress in phosphate metabolism. Hyperphosphatemia and hypophosphatemia]

Serum inorganic phosphate (Pi) concentrations are generally maintained at 2.5-4.5 mg/dL in adults. In children, serum Pi levels are higher than those in adults. Hyperphosphatemia may be the consequence of (1) a decreased excretion of Pi, or (2) an external or internal cause of acute Pi loading to extracellular fluid, and the chronic kidney disease (CKD) is the most frequent cause of hyperphosphatemia. Hyperphosphatemia due to the increased Pi reabsorption is associated with hyperparathyroidism, tumoral calcinosis, and so on. Hypophosphatemia may be caused by (1) a decreased Pi intake, (2) an increased excretion of Pi, or (3) the transcellular shift of Pi from the extracellular to the intracellular space. Hypophosphatemia due to the increased excretion of Pi can be observed in various diseases, including Fanconi syndrome, hereditary hypophosphatemic rickets/osteomalacia, and tumor-induced hypophosphatemic osteomalacia.