Reasons, Preparation and Procedure For Conducting a Creatinine Clearance Test

Submitted on March 27, 2012

Creatinine Clearance Test

Creatinine is product of the breakdown of creatine phosphate, an important part of muscle tissues. This creatine is then passed into the blood, from which it is filtered out by the kidneys. Since the body produces the creatinine at a constant rate, any fluctuations in blood levels can indicate a problem with the kidney function. Typically, the creatinine clearance test compares creatinine levels in the urine to that in the blood. This test also helps to determine the filtration rate of the kidneys. The rate of flow of filtered fluids through the kidneys is measured using the glomerular filtration rate (GFR). There is a strong link between creatine clearance and eGFR (estimated GFR). This is because the creatinine clearance rate allows doctors to arrive at the eGFR by using standard formulas that include factors such as age, sex, weight, race, and height.

Why Is it Done?

A creatinine clearance test can be a very useful diagnostic tool in monitoring kidney function in patients known to have chronic kidney disease or cardiovascular conditions. This can help to decide when kidney dialysis is required for long-term care. It is also helpful in measuring the eGFR to determine if the kidneys are functioning properly and in determining renal failure in patients.

How To Prepare For It?

There are no special requirements, though some doctors may ask for a six-hour fast before the blood sample is taken. Patients will also need to bring a 24-hour urine sample. This consists of all the urine produced in the day and night leading up to the test.

How is it Done?

Blood samples are drawn using normal procedures, similar to those used in blood donation. The laboratory then measures creatinine levels in both - the blood and urine samples. The creatinine clearance rate values are then calculated, with healthy males usually showing values of 100 to 140 ml/min, while females show 90 to 130 ml/min. These values are then used to calculate the eGFR, which is a better indicator of kidney function since it includes several other factors such as age and race.

According to the National Kidney Foundation (NKF), normal eGFR values lie between 90 to 120 ml/min. A test result of below 60 ml/L indicates some level of kidney damage, while a level below 20 ml/min usually indicates renal failure. However, certain conditions such as pregnancy can cause a slight increase in eGFR values. If these values are abnormal, you may be advised to undergo a more accurate measured clearance test to arrive at the actual GFR.