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Creatinine

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Also known as: Creat; Blood Creatinine; Serum Creatinine; Urine Creatinine
Formal name: Creatinine

At a Glance

Why Get Tested?

To determine if your kidneys are functioning normally and to monitor treatment for kidney disease

When to Get Tested?

Routinely as part of a comprehensive or basic metabolic panel; when your doctor suspects that you are suffering from kidney dysfunction or when you are acutely or chronically ill with a condition that may affect your kidneys and/or be worsened by kidney dysfunction; at intervals to monitor treatment for kidney disease or kidney function while on certain medications

Sample Required?

A blood sample drawn from a vein in your arm and/or a 24-hour urine sample

Test Preparation Needed?

You may be instructed to fast overnight or refrain from eating cooked meat; some studies have shown that eating cooked meat prior to testing can temporarily increase the level of creatinine.

The Test Sample

What is being tested?

This test measures the amount of creatinine in the blood and/or urine. Creatinine is a waste product produced by muscles from the breakdown of a compound called creatine. Creatine is part of the cycle that produces energy needed to contract muscles. Both creatine and creatinine are produced by the body at a relatively constant rate. Almost all creatinine is excreted by the kidneys, so blood levels are usually a good indicator of how well the kidneys are working. The quantity produced depends on the size of the person and their muscle mass. For this reason, creatinine concentrations will be slightly higher in men than in women and children.

Results from a blood creatinine test and a 24-hour urine creatinine test may be used to calculate creatinine clearance.

How is the sample collected for testing?

A blood sample is drawn from a vein in the arm. A 24-hour urine sample may also be collected. The doctor or laboratory will provide a large container and instructions for proper sample collection. Typically, the first morning urine sample is not collected, but the time is recorded and used as the start time for the 24-hour collection. All urine produced during the next 24 hours is saved.

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?

You may be instructed to fast overnight or refrain from eating cooked meat; some studies have shown that eating cooked meat prior to testing can temporarily increase the level of creatinine. If a 24-hour urine sample is being collected, it is important to save all of the urine produced during that time period.

The Test

Common Questions

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Article Sources

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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

Horowitz, G. (Updated 2012 October 23). Creatinine. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2054342-overview through http://emedicine.medscape.com. Accessed November 2012.

Dugdale, D. (Updated 2011 August 20). Creatinine – blood. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003475.htm. Accessed November 2012.

(© 1995-2012). Creatinine with Estimated GFR (MDRD), Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/8472 through http://www.mayomedicallaboratories.com. Accessed November 2012.

Dugdale, D. (Updated 2011 August 21). Creatinine – urine. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003610.htm. 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 326-328.

Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 362-363.

Sources Used in Previous Reviews

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.

Physician's Reference Laboratory: Kidney Function Panel. Available online at http://www.prlnet.com/Kidney.htm through http://www.prlnet.com.

(Update: 10/22/2007) MedlinePlus Medical Encyclopedia. Creatinine, Serum. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003475.htm. Accessed November 2008.

(Update: 10/22/2007) MedlinePlus Medical Encyclopedia. Creatinine, Urine. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003610.htm. Accessed November 2008.

(Update: 9/4/2007) MedlinePlus Medical Encyclopedia. Creatinine clearance. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003611.htm. Accessed November 2008.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Pp. 311-312.

National Kidney Foundation. Chronic Kidney Disease. Available online at http://www.kidney.org/kidneyDisease/ckd/index.cfm#whatare through http://www.kidney.org. Accessed January 2009.

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006 Pp. 206-209.

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