The 24-hour Urine Phosphorus test measures the amount of phosphorus excreted in the urine over a 24-hour period. This test helps evaluate phosphorus metabolism, kidney function, and calcium balance in the body. Abnormal phosphorus levels can indicate kidney disorders, bone diseases, or imbalances in parathyroid hormone function, aiding in the diagnosis and management of conditions like hyperparathyroidism and osteoporosis.