What is being tested?The microalbumin test is an early indicator of
kidney failure. It measures the tiny amounts of albumin that the body begins to release into the urine several years before significant kidney damage becomes apparent. Albumin is a protein that is produced in the liver. It is present in high concentrations in the blood, but when the kidneys are functioning properly, virtually no albumin is allowed to leak through into the urine. If a person’s kidneys become damaged or diseased, however, they begin to lose their ability to filter proteins out of the urine. This is frequently seen in chronic diseases, such as
diabetes and
hypertension, with increasing amounts of protein in the urine reflecting increasing kidney failure.
Since the albumin molecule is small, it is one of the first proteins to be detected in the urine with kidney damage. Patients who have consistently detectible amounts of albumin in their urine (microalbuminuria) have an increased risk of developing progressive kidney failure and cardiovascular disease in the future. Because the amount of albumin in the urine varies throughout the day, the most accurate microalbumin measurement is the 24-hour urine test. This test, which requires the collection of all urine over a 24-hour period, is cumbersome and relies on patient compliance. In the case of young children, it can be difficult or impossible to conduct without the use of a catheter. Since not collecting all of the urine will affect the accuracy of the 24-hour test, doctors have begun to order timed (4 hour or overnight) or random (spot) microalbumin tests as an alternative.
Although timed urine samples are not as reliable as 24-hour samples, they can be corrected using creatinine measurement. Creatinine, a byproduct of muscle metabolism, is normally excreted into the urine on a consistent basis. Its level in the urine is relatively stable. Since the concentration (or dilution) of urine varies throughout the day, this property of creatinine allows its measurement to be used as a corrective factor in random urine samples. When a creatinine measurement is performed along with a random microalbumin, the resulting microalbumin/creatinine ratio approaches the accuracy of the 24-hour microalbumin test without the extended collection hassle.
How is the sample collected for testing?You will be asked to collect either a
random sample of urine while you are at the doctor's office or laboratory, a
timed urine sample (such as 4 hours or overnight), or you may be requested to collect a complete
24-hour urine sample. Your doctor or the laboratory will give you a container and instructions for properly collecting a timed or 24-hour urine sample.
