Test Details: The phosphorus 24 hour urine test measures the amount of phosphorus in a sample of urine collected over 24 hours. This test aids in evaluation of hypo- or hyper-phosphatemic states. Factors that increase urinary phosphorus excretion include high phosphorus diet and renal disorders with proximal tubule defects (eg, Fanconi Syndrome, X-linked hypophosphatemic Rickets, tumor-induced osteomalacia). Factors that are associated with decrease in urinary phosphorus excretion include low dietary phosphorus intake, high dietary potassium intake, and conditions associated with decreased intestinal absorption of phosphorus.