The phosphate urine test measures the amount of phosphate in a sample of urine collected over 24 hours (24-hour urine test). Phosphate is a charged particle (ion) that contains the mineral phosphorus. The body needs phosphorus to build and repair bones and teeth, help nerves function, and make muscles contract. Most (about 85%) of the phosphorus contained in phosphate is found in bones. The rest of it is stored in tissues throughout the body.
Urinary phosphorus concentration is useful to assess phosphorus balance. Thyroid and kidneys are key organs whose function influences urinary excretion. This test is also used to identify phosphorus as a possible cause of kidney stones. Many other medical conditions affect urinary phosphorus levels. High urine phosphate levels may be caused by kidney diseases, an overactive parathyroid gland, an too much vitamin D in the body. Low urine phosphate levels may be caused by an underactive parathyroid gland, kidney or liver diseases and malnutrition.