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.
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.
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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.