Creatinine clearance test is done in order to detect creatinine levels in the person. This in turn determines the working of kidneys. Creatinine is one of the waste products that is present in the urine. Presence of this material will help to know how well kidneys are functioning, blood flow and if there are any other disorders that will affect kidneys. This test will determine the rate of blood flow which is known as Glomerular Filtration Rate (GFR). This test is done by taking sample of urine for 24 hours or else sample of blood. GFR varies according to age, gender and size of the person.