Creatinine

Also Known As

Creat

Blood Creatinine

Serum Creatinine

Urine Creatinine

This article was last reviewed on

October 24, 2019.

This article waslast modified on August 12, 2020.

At a Glance

Why Get Tested?

To evaluate the health of your kidneys; to help diagnose kidney disease; to monitor treatment for kidney disease

When To Get Tested?

Routinely as part of a comprehensive metabolic panel (CMP) or basic metabolic panel (BMP) when you have a health exam; when your have signs and symptoms that may be due to kidney disease or damage or when you have 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 is drawn from a vein in your arm. A 24-hour urine sample may also be collected, in which all urine is saved for 24 hours. Sometimes a single, random urine sample may be collected and tested.

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. If a 24-hour urine sample is being collected, it is important to save all the urine produced during that time period.

What is being tested?

Creatinine is a waste product produced by muscles from the breakdown of a compound called creatine. Creatinine is removed from the body by the kidneys, which filter almost all of it from the blood and release it into the urine. This test measures the amount of creatinine in the blood and/or urine.

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. Since almost all creatinine is filtered from the blood by the kidneys and released into the urine, blood levels are usually a good indicator of how well the kidneys are working. The amount of creatinine you produce depends on your body size and your muscle mass. For this reason, creatinine levels are usually slightly higher in men than in women and children.

The kidneys are a pair of bean-shaped organs that are located at the bottom of the ribcage in the right and left sides of the back. Within them are about a million tiny blood filtering units called nephrons. In each nephron, blood is continually filtered through a microscopic cluster of looping blood vessels, called glomerulus. The glomerulus allows the passage of water and small molecules but retains blood cells and larger molecules. Attached to each glomerulus is a tiny tube (tubule) that collects the fluid and molecules that pass through the glomerulus and then reabsorbs what still can be used by the body. The remaining waste forms urine.

Results from a blood creatinine test may be used in combination with results from other tests, such as a 24-hour urine creatinine test, to calculate values that are used to evaluate kidney function.

Common Questions

How is the test used?
The creatinine blood test is used to assess kidney function. It is frequently ordered along with a BUN (blood urea nitrogen) test as part of a basic or comprehensive metabolic panel (BMP or CMP), groups of tests that are done to evaluate the health of your major organs. A BMP or CMP may be used to screen people during routine physical exams or to help evaluate people who seek medical care in the emergency room and/or are admitted to the hospital. Sometimes, creatinine may be performed as part of a renal panel to evaluate kidney function.

If the creatinine and BUN tests are found to be abnormal or if you have an underlying disease that is known to affect the kidneys, such as diabetes or high blood pressure, then creatinine and BUN tests may be used to monitor your kidney function and the effectiveness of treatment.

Blood creatinine and BUN tests may also be ordered to evaluate kidney function prior to some procedures, such as a CT (computed tomography) scan, that may require the use of drugs that can damage the kidneys if not cleared rapidly.

Results from creatinine tests may be used to estimate the amount of blood filtered per minute by the kidneys. This is known as the estimated glomerular filtration rate (eGFR). GFR is difficult to measure directly. Estimated GFR is used to screen for and detect early kidney damage, to help diagnose chronic kidney disease (CKD), and to monitor kidney status.

Blood creatinine measurements, along with age, race, and sex, are used to calculate the eGFR. The National Kidney Disease Education Program, American Society of Nephrology, and the National Kidney Foundation all recommend that an eGFR be calculated every time a creatinine blood test is done.

Another, less common way to obtain GFR is to calculate creatinine clearance. 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 a 24-hour urine sample, and the 24-hour urine volume.

Urine creatinine may also be used with a variety of other urine tests as a correction factor. The concentration (or dilution) of urine varies throughout the day, with more or less liquid being released in addition to the body's waste products. Since creatinine is produced and removed at a relatively constant rate, the amount of urine creatinine can be compared to the amount of another substance being measured. Examples include:

Urine albumin to creatinine ratio (ACR). This calculation more accurately determines how much albumin is escaping from the kidneys into the urine. It is used to screen people with chronic conditions such as diabetes and high blood pressure (hypertension) that put them at an increased risk of developing kidney disease.

Urine protein to creatinine ratio (UP/CR). This calculation may be used to monitor a person with known kidney disease or damage or to screen people on a regular basis when they are taking a medication that may affect their kidney function.
When is it ordered?
Creatinine may be ordered during a routine health exam. It may also be ordered when your healthcare practitioner suspects that your kidneys are not working properly due to your signs and symptoms. Some signs and symptoms of kidney dysfunction include:

Fatigue, lack of concentration, poor appetite, or trouble sleeping

Swelling or puffiness, particularly around the eyes or in the face, wrists, abdomen, thighs or ankles

Urine that is foamy, bloody, or coffee-colored

A decrease in the amount of urine

Problems urinating, such as a burning feeling or abnormal discharge during urination, or a change in the frequency of urination, especially at night

Mid-back pain (flank), below the ribs, near where the kidneys are located

High blood pressure

The creatinine blood test may be ordered, along with a BUN test and urine albumin, at regular intervals when you have a known kidney disorder or a disease that may affect kidney function.

Both BUN and creatinine may be ordered when a CT scan is planned, prior to and during certain drug therapies, and before and after dialysis to monitor the effectiveness of treatments.
What does the test result mean?
Results of creatinine tests are interpreted along with BUN results, and with other tests results that may have been performed at the same time, such as a renal panel.

BUN and creatinine levels that are within the ranges established by the laboratory performing the test suggest that your kidneys are functioning as they should.

Increased creatinine and BUN levels in the blood may mean that your kidneys are not working as they should. Your healthcare practitioner will consider other factors, such as your medical history and physical exam, to determine what, if any, condition may be affecting your kidneys.

Some examples of conditions that can increase creatinine levels include:

Damage to or swelling of blood vessels in the kidneys (glomerulonephritis) caused by, for example, infection or autoimmune diseases

Bacterial infection of the kidneys (pyelonephritis)

Death of cells in the kidneys' small tubes (acute tubular necrosis) caused by, for example, drugs or toxins

Conditions that can block the flow of urine in the urinary tract, such as prostate disease or kidney stone

Reduced blood flow to the kidney due to shock, dehydration, congestive heart failure, atherosclerosis, or complications of diabetes

Low blood levels of creatinine are not common and are not usually a cause for concern. They can be seen with conditions that result in decreased muscle mass. Levels of 24-hour urine creatinine are evaluated with blood levels as part of a creatinine clearance test.

Single, random urine creatinine levels have no standard reference ranges. These results are usually used as references for other substances measured in the urine and to calculate ratios. For example urine albumin results are compared to urine creatinine and a urine albumin/creatinine ratio (ACR) is calculated to provide a more accurate indication of the how much albumin is being released into the urine. Elevated urine albumin may indicate kidney damage, but since the amount of albumin in the urine can vary considerably, an elevated ACR should be repeated twice within 3 to 6 months to confirm the diagnosis.
My creatinine result is slightly out of range. What does this mean?

Your creatinine result is interpreted by your healthcare provider within the context of other tests that you have had done as well as other factors, such as your medical history. A single result that is slightly high or low may or may not have medical significance. This is why a healthcare practitioner may repeat a test on you and why they may look at results from prior times when you had the same test performed.

However, a result outside the range may indicate a problem and warrant further investigation. Your healthcare provider will evaluate your test results in the context of other relevant factors to determine whether a result that falls outside of the reference range means something significant for you.

For more, read the article Reference Ranges and What They Mean.
Will exercise affect my creatinine levels?

In general, moderate exercise will not affect your creatinine levels. As you continue to exercise and build muscle mass, your creatinine levels may increase slightly but not to abnormal levels.
How does diet affect creatinine levels?

Some studies have shown that eating cooked meat prior to testing can temporarily increase the level of creatinine. Creatinine levels may be 10%-30% higher in people who eat a diet that is very high in meat.
What can I do to make my creatinine level normal?

Creatinine is a reflection of processes that are going on in your body and of kidney function. It is not generally responsive to lifestyle changes. If you have an elevated creatinine that is due to a temporary condition, such as a kidney infection, then it should return to normal as the infection resolves. If it is elevated due to an underlying chronic condition that can affect kidney function, such as diabetes, then it will reflect changes in kidney function and is likely to stabilize if or when the condition is under control.
What is creatine? If I take creatine, will my creatinine levels go up?

Creatine is a compound that is made primarily in the liver and then transported to your muscles, where it is used as an energy source for muscle activity. Once in the muscle, some of the creatine is spontaneously converted to creatinine. The amount of both creatine and creatinine depend on muscle mass, so men usually have higher levels than women. Creatine is now available as a dietary supplement. If you take creatine, your creatinine levels may be higher than when you do not take the supplement. You should tell your healthcare provider about all of the dietary supplements you are taking to help in the evaluation of your lab results.
Do creatinine levels change with age?

Creatinine levels relate to both muscle mass and to kidney function. As you age, your muscle mass decreases but your kidneys tend to function less effectively. The net result is not much change in creatinine levels in the blood as you get older.
What is a BUN/Creatinine ratio?

Occasionally, a healthcare practitioner will look at the ratio between a person's BUN and blood creatinine to help determine what is causing these concentrations to be higher than normal. The ratio of BUN to creatinine is usually between 10:1 and 20:1. An increased ratio may be due to a condition that causes a decrease in the flow of blood to the kidneys, such as congestive heart failure or dehydration. It may also be seen with increased protein, from gastrointestinal bleeding, or increased protein in the diet. The ratio may be decreased with liver disease (due to decrease in the formation of urea) and malnutrition.
Why would a urine creatinine be ordered along with a urine drug test?

When people are having drugs-of-abuse testing performed, they may try to "trick the system" by diluting their urine with water (directly or by drinking lots of water) or by adding another adulterating substance to the urine. Since creatinine is produced and released into the urine at a constant rate, it should be present in a normal concentration. The test can be ordered, along with other tests such as a pH and specific gravity and/or tests for adulterants, to help evaluate the validity of a urine sample. If the creatinine is lower than typically seen in a human urine, then it is more likely that the sample has been tampered with or that the person has had too much water to drink. In both of these cases, the urine sample will not be considered suitable for testing and will need to be recollected.
Is there anything else I should know?

Creatinine blood levels can increase temporarily as a result of muscle injury and are generally slightly lower during pregnancy.

Some drugs may cause increased creatinine levels. Inform your healthcare provider of any drugs you are taking.

See More Common Questions See Less Common Questions

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Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

Blood Creatinine Reference Range

The reference ranges¹ provided here represent a theoretical guideline that should not be used to interpret your test results. Some variation is likely between these numbers and the reference range reported by the lab that ran your test. Please consult your healthcare provider.

AGE/GENDER	CONVENTIONAL UNITS²	SI UNITS³
0-18 years	Not available due to wide variability. See child's lab report for reference range.
18-60 years
Male	0.9 - 1.3 mg/dL	80 - 115 µmol/L
Female	0.6 - 1.1 mg/dL	53 - 97 µmol/L
60-90 years
Male	0.8 - 1.3 mg/dL	71 - 115 µmol/L
Female	0.6 - 1.2 mg/dL	53 - 106 µmol/L

¹ from Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. 5th edition, St. Louis: Elsevier Saunders; 2011.

² Conventional Units are typically used for reporting results in U.S. labs

³ SI Units are used to report lab results outside of the U.S.

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Health Professionals – LOINC

LOINC Observation Identifiers Names and Codes (LOINC®) is the international standard for identifying health measurements, observations, and documents. It provides a common language to unambiguously identify things you can measure or observe that enables the exchange and aggregation of clinical results for care delivery, outcomes management, and research. Learn More.

Listed in the table below are the LOINC with links to the LOINC detail pages. Please note when you click on the hyperlinked code, you are leaving Lab Tests Online and accessing Loinc.org.

LOINC	LOINC Display Name
20624-3	Creatinine (24H U) [Mass/Vol]
38483-4	Creatinine (Bld) [Mass/Vol]
21232-4	Creatinine (BldA) [Mass/Vol]
2160-0	Creatinine [Mass/Vol]
2161-8	Creatinine (U) [Mass/Vol]
30004-6	Creatinine Test strip (U) [Mass/Vol]
2162-6	Creatinine (24H U) [Mass/Time]
25886-3	Creatinine (24H U) [Moles/Vol]
59826-8	Creatinine (Bld) [Moles/Vol]
77140-2	Creatinine (S/P/Bld) [Moles/Vol]
14682-9	Creatinine [Moles/Vol]
14683-7	Creatinine (U) [Moles/Vol]
30002-0	Creatinine Test strip (U) [Moles/Vol]
14684-5	Creatinine (24H U) [Moles/Time]

View Sources

Sources Used in Current Review

Arora, P. (2019 May 1, Updated). Chronic Kidney Disease. Medscape Nephrology. Available online at https://emedicine.medscape.com/article/238798-overview. Accessed August 2019.

Gulati, S. (2018 February 21, Updated). Chronic Kidney Disease in Children. Medscape Pediatrics: General Medicine. Available online at https://emedicine.medscape.com/article/984358-overview. Accessed August 2019.

Shah, A. (2019 April, Revised). Evaluation of the Renal Patient. Merck Manual Professional Version. Available online at https://www.merckmanuals.com/professional/genitourinary-disorders/approach-to-the-genitourinary-patient/evaluation-of-the-renal-patient?query=creatinine. Accessed August 2019.

(© 2000-2019). Specimen validity testing. Quest Diagnostics. Available online at https://www.questdiagnostics.com/home/companies/employer/drug-screening/products-services/specimen-validity.html. Accessed August 2019.

Martin, L. et. al. (2017 July 15, Updated). Creatinine blood test. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/003475.htm Accessed August 2019.

Martin, L. et. al. (2017 July 15, Updated). Creatinine urine test. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/003610.htm. Accessed August 2019.

Martin, L. et. al. (2017 July 15, Updated). Creatinine clearance test. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/003611.htm. Accessed August 2019.

(2017 October 1). Mandatory Guidelines for Federal Workplace Drug Testing Programs. Federal Register, Substance Abuse and Mental Health Services Administration Notice. Available online at https://www.federalregister.gov/documents/2017/01/23/2017-00979/mandatory-guidelines-for-federal-workplace-drug-testing-programs. Accessed August 2019.

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.

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.

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.

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.

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

(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. 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.

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

Horowitz, G. (2014 December 10, Updated). Creatinine. Medscape Drugs & Diseases [On-line information]. Available online at http://emedicine.medscape.com/article/2054342-overview. Accessed 07/18/15.

Delgado, J. and Straseski, J. (2015 May). Renal Function Markers - Kidney Disease. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/RenalFunctionMarkers.html. Accessed 07/18/15.

Salazar, J. (2014). Overview of Urea and Creatinine. Medscape Multispecialty from Lab Med. 2014;45(1):e19-e20. [On-line information]. Available online at http://www.medscape.com/viewarticle/823420. Accessed 07/18/15.

Dugdale, D. (2013 August 4, Updated). Creatinine blood test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003475.htm. Accessed 07/18/15.

Dugdale, D. (2013 August 25, Updated). Creatinine - urine. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003610.htm. Accessed 07/18/15.

Nair S, et al. Effect of a cooked meat meal on serum creatinine and estimated glomerular filtration rate in diabetes-related kidney disease. Published online before print September 23, 2013, doi: 10.2337/dc13-1770 Diabetes Care. Available online at http://care.diabetesjournals.org/content/early/2013/09/16/dc13-1770.full.pdf+html. Accessed August 2013.

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