Phosphorus is mainly stored in the bones. It plays a crucial role in various biological processes, including energy production, bone mineralisation and maintaining the integrity of cell membranes.

The kidneys are responsible for maintaining a phosphorus balance by regulating its reabsorption and excretion.
Phosphorus levels are closely regulated by the parathyroid hormone (PTH). In conditions such as hyperparathyroidism, PTH increases urinary phosphorus excretion, while in hypoparathyroidism, urinary phosphorus excretion may decrease.

Osteomalacia and rickets may be associated with a loss of phosphate in the urine, often due to defects in phosphate reabsorption.

Urinary phosphorus measurements are generally used in conjunction with serum calcium and phosphorus levels to assess overall mineral balance, particularly in patients with metabolic bone disease, hypercalcaemia or those undergoing dialysis. Disturbances in phosphocalcium balance can have an impact on the risk of cardiovascular disease, calcification and bone health.