Phosphorus (inorganic phosphate) is an essential compound for many functions (energy metabolism, bone formation, etc.). Surplus phosphorus is eliminated by the kidneys under the influence of several factors including diet, quality of intestinal absorption, medications (antacids, etc.), parathyroid gland function, vitamin D levels and certain specific kidney diseases. Urine phosphorus levels are mainly useful for investigating abnormal blood phosphorus levels (phosphatemia) and kidney stones. Results are expressed in millimoles of phosphorus per day (mmol/d) for a 24-hour urine collection and in millimoles of phosphate per millimole of creatinine (mmol/mmol creatinine) for an isolated urination. Urine phosphorus levels are interpreted in light of blood phosphorus levels and other clinical information.
The risk of the formation of calcium phosphate stones is assessed not only in light of urine phosphate and calcium levels, but also based on other factors that contribute to stone formation (dehydration, kidney function, urinary tract infections and certain medications, etc.) or factors that prevent their formation (citrate level).