At a glance

Why get tested?

To diagnose kidney malfunction if the eGFR (estimate of glomerular filtration rate) is unsuitable

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, dehydration, shock, or another disease, such as congestive heart failure. The most common test for kidney function is serum creatinine and the eGFR, however in some patients further testing is required.

Sample required?

Both a urine sample (24-hour collection) and a blood sample drawn from a vein in your arm

What is being tested?

Creatinine is a chemical derived from creatine, a nitrogen-containing 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 plasma. The results are a measure of kidney function.

How is the sample collected for testing?

The test requires a 24-hour urine collection and a blood sample drawn either at the beginning or end of the urine collection. The blood sample is drawn by needle from a vein in the arm.

The Test

How is it used?

Creatinine is normally filtered through the glomerulus - a group of blood vessels in the kidneys responsible for filtration. An abnormal kidney function test indicates that the patient may have lost more than 30-40% of his or her kidney's function, which may be a permanent or temporary loss.

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, shock, 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.

What does the test result mean?

Looking for reference ranges?

A decreased filtration rate 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, dehydration, shock, obstruction within the kidney, or acute or chronic kidney failure are among the possible causes.

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.

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 Australia include the calculation of estimated glomerular function rate (eGFR) from a single blood sample taken from a vein in your arm.

Common Questions

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 call either your doctor or the laboratory where you obtained your container to ask if you should discontinue the test and begin again another day.

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 tracer and are more expensive. For most medical purposes, the accuracy of the eGFR is sufficient however creatinine clearance may be useful in patients with abnormal body composition, diet or other factors.

Can I perform this test at home?

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

Last Review Date: March 25, 2013