The 24-Hour Urine Creatinine test measures the amount of creatinine excreted in the urine over a 24-hour period. Creatinine is a waste product produced by muscle metabolism, and its excretion is generally consistent. This test is often used to assess kidney function by comparing the amount of creatinine in urine with other substances or to evaluate how well the kidneys are clearing creatinine from the bloodstream. It is commonly used in conjunction with other kidney function tests, such as the creatinine clearance test, to estimate the glomerular filtration rate (GFR) and monitor the progression of kidney disease or other renal conditions.