Creatinine Clearance Test

What is the creatinine clearance test?

The creatinine clearance test is done to check how well your kidneys are working.

Creatinine is made in the muscles as your body produces energy. It is carried by the blood to the kidneys, which filter it from the body into the urine.

The creatinine clearance test compares the level of creatinine in a 24-hour sample of urine with the creatinine level in the blood. Your healthcare provider can then determine how well your kidneys are filtering.

Why is this test done?

The creatinine clearance test is done to:

• See how well the kidneys are functioning.
• Check for kidney failure (this test is one of the most sensitive tests for kidney failure).
• Monitor kidney function if you have a chronic disease such as diabetes and some autoimmune diseases.
• Predict the rate of kidney failure so your healthcare provider can know when you may need kidney dialysis.
• Adjust medicine doses when the kidneys are failing.

How do I prepare for this test?

• You don't need to fast before the test. You should eat and drink as you usually would.
• It is 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. Don't stop any of your regular medicines without first consulting with your healthcare provider.
• Talk to your healthcare provider if you have any questions.

How is this test done?

To collect the urine sample: Urinate into the toilet after you get up on the day you start the test (Day One). After that, collect all of the urine you pass for the next 24 hours. (You'll be given a container to put the urine in.) Keep the urine cool by storing it in the refrigerator. On the second day of the test (Day Two), urinate into the container in the morning when you get up, cap the container, and take it to the lab.

At the lab a small amount of blood is taken from your arm with a needle and collected in tubes. There is no risk of contracting AIDS, hepatitis, or any other blood-borne diseases from this procedure.

How will I get the test result?

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

What does the test result mean?

Normal values for creatinine clearance are:

• men: 85 to 125 milliliters per minute (mL/min)
• women: 75 to 115 mL/min.

The normal ranges are lower than the values listed above for older adults due to a normal decrease in kidney function as people age. The normal ranges may also vary slightly from lab to lab. Normal ranges are usually shown next to your results in the lab report.

A creatinine clearance lower than normal usually means that one or both kidneys aren't working normally. There are three reasons your kidneys might have problems:

• Your kidneys might not be getting enough blood. Sometimes this happens because there is a blockage in the blood vessels going to the kidneys.
• Your kidneys might be diseased or damaged. Examples of this include damage from high blood pressure, diabetes, infections, or autoimmune diseases.
• If the flow of urine from a kidney is blocked, the kidney can become damaged over time. This type of blockage might be caused by a kidney stone or by a kink in the tube going away from the kidney or from something pressing down on the tube, such as an enlarged prostate gland or a tumor.

Some medicines can affect the results of the creatinine clearance test, such as:

• certain blood pressure medicines including ACE inhibitors (such as captopril and enalapril)
• nonsteroidal anti-inflammatory drugs (such as ibuprofen or naproxen)
• diuretics (water pills), such as furosemide
• some antibiotics including aminoglycosides (for example, gentamicin) and cephalosporins (for example, cefoxitin).

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.

If your test results are abnormal, ask your healthcare provider:

• if you need additional tests
• what you can do to work toward a normal value
• when you need to be tested again.