Creatinine is a chemical waste product produced by muscle metabolism. When your kidneys are functioning normally, they filter creatinine and other waste products out of your blood. These waste products are removed from your body through urination. A creatinine urine test measures the amount of creatinine in your urine. The test can help your doctor evaluate how well your kidneys are functioning. This is useful for diagnosing or ruling out kidney disease and other conditions affecting the kidneys. Your doctor may use a random urine sample to test for creatinine. However, they’ll order a urine 24-hour volume test in most cases.