Hyperphosphatemia

Serum phosphorus concentrations are maintained within narrow limits in humans. In the extracellular fluid most of the phosphorus is present in the inorganic form and at the level of the glomerulus greater than 90% of PO ₄ is ultrafilterable. The kidney plays a key role in PO ₄ homeostasis. Micropuncture experiments have demonstrated that 60 to 70% of the filtered PO ₄ is reabsorbed in the proximal tubule; however, there is evidence that a significant amount of PO ₄ is reabsorbed in the distal tubule. Phosphate secretion probably plays a minor role in the overall renal regulation of phosphate. In normal individuals the amount of PO ₄ ingested plays a key role in the amount that ultimately will be excreted in the urine. The reabsorption of PO ₄ along the nephron is regulated by a series of factors of which parathyroid hormone is the most important one. Hyperphosphatemia is seen frequently in clinical medicine and by far, the most common cause is a decrease in urinary PO ₄ excretion secondary to renal failure. From the practical point of view, the most effective way to treat hyperphosphatemia is to decrease PO ₄ absorption in the GI tract by the use of PO ₄ binders.