A quantitative test that measures the total amount of creatinine excreted in the urine over a 24-hour period. Since creatinine production primarily depends on lean muscle mass and remains relatively stable for an individual from day to day (if kidney function is stable), this measurement is primarily used to evaluate the completeness of the 24-hour urine collection. It is also essential for calculating creatinine clearance (glomerular filtration rate) when combined with serum creatinine measurements.