At a Glance
Why Get Tested?
To determine the function of your kidneys
When to Get Tested?
As a practical test to look for evidence of kidney damage. For a more definitive assessment of kidney function or to monitor changes in kidney function if you already have kidney disease, measurement of creatinine clearance is preferred.
Creatinine Clearance can be calculated using your age, weight, gender, and serum creatinine (requires a blood sample from a vein in your arm); in some formulas, race is also used in the calculation. Measured Creatinine Clearance, which gives an assessment of Glomerular Filtration Rate (GFR), is calculated from serum and urine creatinine levels and requires a blood sample from a vein in your arm and normally a 24-hour collection of urine.
The Test Sample
What is being tested?
Creatinine Clearance gives an assessment of glomerular filtration rate (GFR) which in turn is a measure of the function of your kidneys. Glomeruli are tiny filters in your kidney that allow waste products to be removed from the blood, while preventing loss of important proteins and blood cells. The rate refers to the amount of blood that is filtered per minute. Calculated creatinine clearance is an estimate of creatinine clearance based on the serum creatinine value only and used when it is either not practical or possible to collect a 24 hr urine.
How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm; your weight and age are needed for calculation of creatinine clearance as well. Measured creatinine clearance requires both a blood sample taken from a vein in your arm and a 24-hour sample of urine.
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.