Creatinine Clearance

Related tests: Creatinine; glomerular filtration rate (GFR); Urinalysis

At a Glance

Why Get Tested?

To diagnose kidney malfunction

When to Get Tested?

If your doctor thinks that you may have a problem affecting the function of your kidneys, such as an obstruction within the kidney, acute or chronic kidney failure, , shock, or another disease, such as congestive heart failure. Creatinine clearance may also be measured before you are prescribed certain drugs which rely on good kidney function in order to allow them to be removed from the body effectively after they have carried out their purpose. Other straightforward methods of estimating the function of your kidneys now in routine use across the UK include the calculation of estimated glomerular function rate (eGFR) from a single blood sample taken from a vein in your arm.

Sample Required?

Both a urine sample () and a blood sample taken from a vein in your arm.

The Test Sample

What is being tested?

Creatinine is a chemical derived from creatine, a nitrogen-based organic compound used by muscles to store and transfer energy. The amount of creatinine produced in the body is dependent on muscle mass and is constant for an individual. It is removed from the body as blood passes through the kidneys. By measuring creatinine in the blood and in the urine, it is possible to determine the amount of blood filtered by the kidneys in a measured period of time. A calculation is made based on the amount of creatinine in the urine, the time period of collection, and the amount of creatinine in the blood serum or .

How is the sample collected for testing?

The test requires a and a blood sample taken either at the beginning or end of the urine collection. The blood sample is collected by needle from a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

The Test

How is it used?

To assess the function of your kidneys.

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When is it requested?

The test may be requested if you suffer from kidney disease or a condition known to effect kidney function such as congestive heart failure, or diabetes. It may also be requested to assess kidney function prior to the administration of some toxic drugs as dose may be dependent on kidney function.

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What does the test result mean?

Very approximately, a normal creatinine clearance is 100 mL/minute. You may find it useful to consider your results in percentage terms. For example if your creatinine clearance is 50, then you have lost about 50% of your kidney function. This may be a permanent or temporary loss. A decreased creatinne clearance may indicate a decrease in the amount of blood filtered by the kidney due to disease within the kidney cells or to decreased delivery of blood to the kidneys. Congestive heart failure, diabetes, , shock, obstruction within the kidney, or acute or chronic kidney failure are among the possible causes.

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Is there anything else I should know?

Certain drugs, such as aminoglycosides, cimetidine, cisplatin, and cephalosporins can decrease the creatinine clearance measurement. Diuretics can increase the result.

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Common Questions

1. What should I do if I forget to save one urine sample during the collection?

If you do not have a complete collection, the results will not be valid. You should either call your doctor or the laboratory where you obtained your container to ask if you should discontinue the test and begin again another day.

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2. Is this test extremely accurate?

There are other, more involved tests that have higher accuracy. However, these are more complex for the patient and doctor and involve injecting the patient with a and are more expensive. For most medical purposes, the accuracy of creatinine clearance is sufficient. Very similar information to that produced by the more complex tests can be obtained using estimated GFR, which does not require a urine collection. Creatinine clearance measurement is new rarely necessary in clinical practice.

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3. Can I perform this test at home?

No. The test requires analysis and calculations by skilled personnel.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.