What is being tested?
Creatinine Clearance gives an assessment of glomerular filtration rate (GFR) which in turn is a measure of the function of your kidneys. Glomeruli are tiny filters in your kidney that allow waste products to be removed from the blood, while preventing loss of important proteins and blood cells. The rate refers to the amount of blood that is filtered per minute. Calculated creatinine clearance is an estimate of creatinine clearance based on the serum creatinine value only and used when it is either not practical or possible to collect a 24 hr urine.

How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm; your weight and age are needed for calculation of creatinine clearance as well. Measured creatinine clearance requires both a blood sample taken from a vein in your arm and a 24-hour sample of urine.