Creatinine Clearance Test

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KEY POINTS

• The creatinine clearance test is done to see how well your kidneys are working. It can help diagnose and treat kidney disease.
• This test requires both a 24-hour urine collection and a blood test. The blood test is done either right before you start to collect urine or the day you finish collecting urine. The samples are then sent to a lab.
• Talk to your healthcare provider about what the test results mean and ask any questions you have.

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What is the creatinine clearance test?

This test measures and compares the level of creatinine in your urine with the level of creatinine in your blood. The test is done on the amount of urine your body makes in 24 hours.

Muscles make creatinine when another chemical, creatine, is broken down to produce energy for the muscles. This waste product is carried by the blood to the kidneys, which filter it from the body into the urine.

Why is this test done?

This test is done to see how well your kidneys are working. It can help diagnose and treat kidney disease.

How do I prepare for this test?

• It’s best to avoid vigorous exercise during the 24 hours you are collecting the urine because it may affect the results.
• You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Ask your provider before stopping any of your regular medicines.
• Your healthcare provider may ask you not to eat anything and to drink just water for about 8 hours before the blood test.
• Talk to your healthcare provider if you have any questions about the test.

How is this test done?

This test requires both a 24-hour urine collection and a blood test. The blood test is done either right before you start to collect urine or the day you finish collecting urine.

24-Hour Urine Collection

You need to collect and save all of the urine you make in 24 hours. Before you start collecting the urine sample, urinate into the toilet right after you get up on the day you start the test. Then collect all of the urine you pass in a container for the next 24 hours. Keep the urine cool by storing it capped in the refrigerator or in another cool place. On the second day of the test, get your last sample of urine when you get up, cap the container, and take it to the lab.

Blood Test

A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your healthcare provider when and how you will get the results of your test.

What does the test result mean?

A creatinine clearance lower than normal usually means that one or both kidneys are not working well, either because of disease, damage, or a blockage in your urinary system. Some medicines can affect the results of the creatinine clearance test. Ask your healthcare provider about this.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about your result and ask questions, such as:

• If you need more tests
• What kind of treatment you may need
• What lifestyle, diet, or other changes you might need to make