What is being tested?This test measures the amount of creatinine in the blood and urine to help evaluate the kidneys’ filtering ability. Creatinine is a waste product derived from creatine, a nitrogen-based organic compound used by muscles to store and transfer energy. The amount of creatinine produced in the body is dependent on muscle mass and is constant for an individual. It is removed from the body by filtering units called
glomeruli as blood passes through the kidneys. The amount of creatinine taken from the blood depends on the filtering ability of the glomeruli and the rate at which blood is carried to the kidneys. If the glomeruli are damaged or diseased, or if blood circulation is slowed, then less creatinine will be removed from the blood and released into the urine.
The creatinine clearance is a calculation that allows a general evaluation of the amount of blood that is being filtered in 24 hours. There are several versions of this calculation. All of them include the measurement of the amount of creatinine in a blood sample collected just before or after the urine collection, the amount of creatinine in 24-hour urine sample, and the 24-hour urine volume. Since the amount of creatinine produced depends on muscle mass, some calculations also use a correction factor that takes into account a patient’s body surface area (their height and weight).
