Urine Albumin and
Albumin/Creatinine Ratio

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Also known as: Microalbumin; ACR; UACR
Formal name: Urine Albumin and Albumin/Creatinine Ratio

At a Glance

Why Get Tested?

To detect early damage to the kidneys in those with diabetes or high blood pressure (hypertension)

When to Get Tested?

Annually after a diagnosis of diabetes or hypertension

Sample Required?

A random, timed, overnight, or 24-hour urine sample

Test Preparation Needed?

None

The Test Sample

What is being tested?

Albumin is a protein made by the liver. The urine albumin test detects and measures the amount of albumin in the urine. A small amount of albumin in the urine is an early indicator of kidney damage. In the past, these small amounts of albumin were referred to as "microalbumin" and some health practitioners may continue to use the term, although it is being phased out.

A urine albumin test is used to screen people with chronic conditions such as diabetes and high blood pressure who are at high risk for kidney damage. It can detect small amounts of albumin that escape from the kidneys into the urine several years before significant kidney damage becomes apparent.

Drawing of a kidney and the urinary tract

Plasma, the liquid portion of blood, contains many different proteins. One of the many functions of the kidneys is to conserve plasma proteins so that they are not excreted along with waste products when urine is produced. There are two mechanisms that normally prevent protein from passing into urine: (1) the glomeruli provide a barrier that keeps most larger plasma proteins inside the blood vessels and (2) the smaller proteins that do get through are almost entirely reabsorbed by the tubules. (For additional details on kidneys and how they function, see the video on  How Kidneys Work on the Davita web site.)

Protein in the urine (proteinuria) most often occurs when either the glomeruli or tubules in the kidney are damaged. Inflammation and/or scarring of the glomeruli can allow increasing amounts of protein to leak into the urine. Damage to the tubules can prevent protein from being reabsorbed.

Albumin is a plasma protein that is present in high concentrations in the blood, and when the kidneys are functioning properly, virtually no albumin is present in the urine. If a person's kidneys become damaged or diseased, however, they begin to lose their ability to conserve albumin and other proteins. This is frequently seen in chronic diseases, such as diabetes and hypertension, with increasing amounts of protein in the urine reflecting increasing kidney failure.

Albumin is one of the first proteins to be detected in the urine with kidney damage. People who have consistently detectable small amounts of albumin in their urine (a condition called microalbuminuria) have an increased risk of developing progressive kidney failure and cardiovascular disease in the future.

Most of the time, both albumin and creatinine are measured in a random urine sample and an albumin/creatinine ratio (ACR) is calculated. This may be done to more accurately determine how much albumin is escaping from the kidneys into the urine. The concentration (or dilution) of urine varies throughout the day with more or less liquid being excreted in addition to the body's waste products. Thus, the concentration of albumin in the urine may also vary. Creatinine, a byproduct of muscle metabolism, is normally excreted into the urine at a constant rate and its level in the urine is an indication of the amount of liquid being excreted as urine. This property of creatinine allows its measurement to be used as a corrective factor in random urine samples. The American Diabetes Association has stated a preference for the ACR for screening for microalbuminuria.

How is the sample collected for testing?

random sample of urine, a timed urine sample (such as 4 hours or overnight), or a complete 24-hour urine sample is collected in a clean container. The health care provider or laboratory will provide a container and instructions for properly collecting the sample that is needed.

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.

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

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Mayo Clinic Staff (Updated 2010 July 31). Microalbumin test. Mayo Clinic [On-line information]. Available online at http://www.mayoclinic.com/print/microalbumin/MY00143/METHOD=print&DSECTION=all through http://www.mayoclinic.com. Accessed April 2012.

Durani, Y. (Reviewed 2012 March). Urine Test: Microalbumin-to-Creatinine Ratio. Nemours [On-line information]. Available online at http://kidshealth.org/parent/system/medical/test_mtc_ratio.html through http://kidshealth.org. Accessed April 2012.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 678-679.

Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 368.

(© 2012) American Diabetes Association. Kidney Disease. Available online at http://www.diabetes.org/living-with-diabetes/complications/kidney-disease-nephropathy.html through http://www.diabetes.org. Acccessed April 2012.

(© 2012) National Kidney Foundation. Microalbuminuria in Diabetic Kidney Disease. Available online at http://www.kidney.org/news/newsroom/fs_new/microalbindbkd.cfm through http://www.kidney.org. Accessed April 2012.

Greg Miller, Ph.D. Professor of Pathology. Director of Clinical Chemistry. Director of Pathology Information Systems. Virginia Commonwealth University.

Sources Used in Previous Reviews

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