The Creatinine test measures the level of creatinine in the blood, a waste product produced by muscle metabolism. This test helps evaluate kidney function, as kidneys are responsible for filtering creatinine out of the blood. Elevated creatinine levels may indicate impaired kidney function or kidney disease. The test is commonly used in routine health checks or for monitoring patients with kidney disorders. It can also be part of a creatinine clearance test that assesses how well kidneys are filtering blood.