Creatinine clearance is a test used to assess how well the kidneys are filtering waste from the blood. It measures the amount of creatinine, a waste product produced by muscle metabolism, in both blood and urine. By comparing these levels, healthcare providers can estimate the glomerular filtration rate (GFR), which indicates kidney function. The test typically involves collecting urine over 24 hours and taking a blood sample. A lower creatinine clearance value may suggest impaired kidney function, while a normal value indicates that the kidneys are working effectively. This information helps in diagnosing and monitoring kidney diseases.