Synonyms:  Urine Creatinine, Random Why It Is Done • Determine whether your kidneys are functioning normally. • Monitor the progress of your kidney disease. • Monitor the kidney function of people who take medications that can cause kidney damage.     Test Overview Creatinine test measure the level of the waste product creatinine in your urine. These tests provide information about how well your kidneys are working. Creatine is a substance that forms when food is converted into energy through a process called metabolism. Creatine is broken down into another substance called creatinine, which is filtered out of your blood by the kidneys and then passed out of your body in urine.  Creatinine is produced at a steady rate and is affected very little by diet or by normal physical activities. If your kidneys are damaged and cannot function normally, the amount of creatinine in your urine decreases while its level in your blood increases.    How To Prepare Avoid strenuous exercise 48 hours prior to having creatinine tests.