Creatinine Clearance

A creatinine clearance test measures the rate at which the kidneys clear creatinine from the blood. Creatinine is a substance that is easily excreted by the kidney in healthy people. Because all the creatinine filtered by the kidneys in a given time interval is excreted into the urine, creatinine levels are equivalent to the glomerular filtration rate (GFR); the rate at which the kidneys process blood through the glomerular system.

A creatinine clearance test compares the serum creatinine with the amount of creatinine excreted in a volume of urine for a specified time. A 24-hour time frame is most common. At the beginning of the test, the patient empties his bladder and the urine is discarded. Then, all urine voided during the specific time period is collected. Sometime during the test period a blood sample is drawn to determine the serum creatinine, so that the amount excreted in the urine and the amount remaining in the blood can be compared. The nurse has an important role in instructing the patient about the purpose of the test and the procedures that will be used.

Expected creatinine clearance values (expressed as number of milliliters per minute per 1.72 meters squared of body surface)

Decreased creatinine clearance

A decrease in the kidney's ability to clear creatinine is an indication of decreased glomerular function.

The creatinine clearance test is used to diagnose renal dysfunction and is also used to evaluate the progression of renal disease. A minimum creatinine clearance of 10ml/min is necessary to maintain life without the use of renal or peritoneal dialysis.

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In a 24 hour creatinine clearance test, the bladder is first emptied and then all the urine produced in 24 hours is collected.