Creatinine, 24-Hour Urine - This test measures the amount of creatinine expelled in the urine over a 24-hour period and is used to evaluate kidney function. This test helps determine how well the kidneys are able to filter small molecules like creatinine out of the blood. It is often used in conjunction with blood creatinine tests to calculate the creatinine clearance rate, which can provide more detailed information on kidney filtration efficiency. This is particularly useful in detecting renal dysfunction and monitoring known kidney disease or conditions affecting kidney performance.