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, , 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.
Both a urine sample () and a blood sample drawn from a vein in your arm
Test preparation needed?
What is being tested?
This test measures the concentration of creatinine in both a sample of blood and a sample of urine from a . The results are used to calculate the amount of creatinine that has been cleared from the blood and passed into the urine over a 24 hour time period.
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 . The results are a measure of kidney function.
Since the amount of creatinine produced depends upon muscle mass, in some circumstances, e.g. in children, the calculation will need to be corrected for body surface area.
How is the sample collected for testing?
The test requires a 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.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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 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 in an accredited laboratory.