Microalbuminuria Test

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?

A 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.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

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