Creatinine Clearance Test

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KEY POINTS

• The creatinine clearance test is done to see how well your child’s 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 child’s 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 child’s urine with the level of creatinine in the blood. The test is done on the amount of urine your child’s 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 child’s kidneys are working. It can help diagnose and guide the treatment of kidney disease.

How do I prepare my child for this test?

• It’s best for your child to avoid vigorous exercise during the 24 hours you are collecting the urine because it may affect the results.
• Your child may need to avoid taking certain medicines before the test because they might affect the test result. Tell your child's healthcare provider about all the medicines and supplements your child takes. Ask your child’s provider before stopping any of your child’s regular medicines.
• Your child’s healthcare provider may ask you not to let your child eat anything and to drink just water for about 8 hours before the blood test.
• Talk to your child’s 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 the urine your child makes in 24 hours. Before you start collecting the urine sample, your child should urinate into the toilet right after getting up on the day you start the test. Then collect all the urine your child passes 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, collect your child’s last sample of urine when your child gets up, cap the container, and take it to the lab.

If you forget to save one urine sample during the collection time, the results will not be accurate. Call your child’s healthcare provider’s office. Stop the test and begin again another day.

Blood Test

A small amount of blood is taken from a vein in your child’s arm with a needle. In younger children, this test can be done with a finger prick or heel stick. The blood is collected in tubes and sent to a lab.

Ask your child’s healthcare provider how and when you will get your child’s test results.

What does the test result mean?

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

What if my child’s test result is not normal?

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

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