At a Glance
Why Get Tested?
To help detect and evaluate kidney dysfunction or decreased blood flow to the kidneys
When to Get Tested?
When your doctor thinks that you may have a problem affecting the function of your kidneys, such as an obstruction within the kidney or acute or chronic kidney failure, or dysfunction due to another disease, such as congestive heart failure
Both a urine sample (24-hour collection) and a blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
This test measures creatinine levels in both a sample of blood and a sample of urine from a 24-hour urine collection. The results are used to calculate the amount of creatinine that has been cleared from the blood and passed into the urine. This calculation allows for a general evaluation of the amount of blood that is being filtered by the kidneys in a 24-hour time period.
Creatinine is a waste product produced in the muscles from the breakdown of a compound called creatine. Creatine is part of the cycle that produces energy needed to contract muscles. The amount of creatinine produced in the body is dependent on muscle mass and is relatively constant for an individual.
Almost all creatinine is removed from the body by the kidneys, so levels in the blood are a good indication of how well the filtering units in the kidneys, called glomeruli, are functioning. The amount of creatinine removed from the blood depends on both the filtering ability of the glomeruli in the kidneys and the rate at which blood is carried to the kidneys.
The amount of blood filtered per minute is known as the Glomerular Filtration Rate (GFR). If the glomeruli are damaged or diseased, or if blood circulation is slowed, then less creatinine will be removed from the blood and released into the urine and the GFR will be decreased.
There are several versions of the creatinine clearance calculation. All of them include the measurement of the amount of creatinine in a blood sample collected just before or after the urine collection, the amount of creatinine in 24-hour urine sample, and the 24-hour urine volume. Since the amount of creatinine produced depends on muscle mass, some calculations also use a correction factor that takes into account a person's body surface area (using their height and weight).
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 person being tested will also usually be asked to provide their current height and weight.
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.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
Ask a Laboratory Scientist
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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.
Sources Used in Current Review
Dugdale, D. (Updated 2011 August 21). Creatinine clearance. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003611.htm. Accessed November 2012.
Medscape Editorial Staff (Updated 2012 October 1). Creatinine Clearance. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2117892-overview through http://emedicine.medscape.com. Accessed November 2012.
(© 1995-2012). Creatinine Clearance. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/8500 through http://www.mayomedicallaboratories.com. Accessed November 2012.
Wilhelm, S. and Kale-Pradhan, P. (2011 July 29). Estimating Creatinine Clearance. Medscape News Today from Pharmacotherapy. 2011;31(7):658-664 [On-line information]. Available online at http://www.medscape.com/viewarticle/746232 through http://www.medscape.com. Accessed November 2012.
Arora, P. (Updated 2012 March 28). Chronic Kidney Disease. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/238798-overview through http://emedicine.medscape.com. Accessed November 2012.
(Updated 2012 March 23). The Kidneys and How They Work. National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC) [On-line information]. Available online at http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/ through http://kidney.niddk.nih.gov. Accessed November 2012.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 329-333.
Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 78-79.
Sources Used in Previous Reviews
Clinical Chemistry: Theory, Analysis, Correlation. 3rd Edition. Lawrence A. Kaplan and Amadeo J. Pesce, St. Louis, MO. Mosby, 1996.
Clinical Chemistry: Principles, Procedures, Correlations. Michael L. Bishop, Janet L. Duben-Engelkirk, Edward P. Fody. Lipincott Williams & Wilkins, 4th Edition.
Mitchell G. Scott, PhD. Division of Laboratory Medicine, Washington University School of Medicine, St. Louis, MO
Martin H. Kroll, MD. Director of Clinical Chemistry, VA Medical Center, Dallas, TX.
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
(2002 March). Medical Tests of Kidney Function. National Kidney and Urologic Diseases Information Clearinghouse, NIH Publication No. 02; 4623 [On-line information]. Available online at http://kidney.niddk.nih.gov/kudiseases/pubs/kidneytests/index.htm through http://kidney.niddk.nih.gov.
Esson, M. and Schrier, R. (2002). Diagnosis and Treatment of Acute Tubular Necrosis. Ann Intern Med 2002;137:744-752 [On-line journal]. PDF available for download at http://www.annals.org/cgi/reprint/137/9/744.pdf through http://www.annals.org.
Agha, Irfan (2004 February 11, Updated). Creatinine - serum. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003475.htm.
Agha, Irfan (2004 February 11, Updated). Creatinine - urine. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003610.htm.
Agha, Irfan (2004 February 11, Updated). Creatinine clearance. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003611.htm.
Agha, Irfan (2003 August 7, Updated). BUN. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003474.htm.
Agrawal, M. and Swartz, R. (2000 April 1). Acute Renal Failure. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20000401/2077.html through http://www.aafp.org.
Nissl, J. (2004 September 20, Updated). Creatinine and Creatinine Clearance WebMD [On-line information]. Available online at http://my.webmd.com/hw/kidney_failure/hw4322.asp through http://my.webmd.com.
Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006, Pp 209-211.
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER and Bruns DE, eds. 4th ed. St. Louis, Missouri: Elsevier Saunders; 2006, Pp 797-798; 818-819.
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC, Pg 43.
(February 2009) National Kidney and Urologic Diseases Information Clearinghouse. The Kidneys and How they Work. Available online at http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/index.htm#tests through http://kidney.niddk.nih.gov. Accessed September 2009.
(Updated September 4, 2007) Silberberg, C. Medline Plus Medical Encyclopedia: Creatinine Clearance. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003611.htm. Accessed September 2009.