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Urine Albumin and
Albumin/Creatinine Ratio

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Also known as: Microalbumin; ACR; UACR
Formal name: Urine Albumin; Albumin-to-Creatinine Ratio

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The Test Sample

What is being tested?

Albumin is a major protein normally present in blood. The urine albumin test detects and measures the amount of albumin in the urine. The presence of a small amount of albumin in the urine may be an early indicator of kidney disease. A small amount of albumin in the urine is sometimes referred to as urine microalbumin or microalbuminuria. "Microalbuminuria" is slowly being replaced with the term "albuminuria," which refers to any elevation of albumin in the urine.

Drawing of a kidney and the urinary tract

Plasma, the liquid portion of blood, contains many different proteins, including albumin. One of the many functions of the kidneys is to conserve plasma proteins so that they are not released 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 large plasma proteins inside the blood vessels and (2) the smaller proteins that do get through are almost entirely reabsorbed by the tubules.

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 dysfunction.

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 (albuminuria) have an increased risk of developing progressive kidney failure and cardiovascular disease in the future.

A urine albumin test is used to screen for kidney disease in people with chronic conditions such as diabetes and high blood pressure. It can detect small amounts of albumin that escape from the blood through the kidneys into the urine several years before significant kidney damage becomes apparent. Most of the time, tests for albumin and creatinine are done on a urine sample collected randomly (not timed) and an albumin-to-creatinine ratio is calculated. This is done to provide a more accurate indication of the how much albumin is being released into the urine. (For more, see "The Test" tab.)

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 practitioner 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.