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