Urine Albumin and Albumin to Creatinine Ratio
Once a diagnosis of type 2 diabetes is made and then annually; 5 years after diagnosis of type 1 diabetes and then annually; at regular intervals when you have high blood pressure
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. Your healthcare practitioner or laboratory will provide a container and instructions for properly collecting the sample that is needed.
Albumin is a major protein normally present in blood, but virtually no albumin is present in the urine when the kidneys are functioning properly. However, albumin may be detected in the urine even in the early stages of kidney disease. The urine albumin test (formerly called microalbumin) detects and measures the amount of albumin in the urine to screen for kidney disease.
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 (ACR) is calculated. This is done to provide a more accurate indication of the how much albumin is being released into the urine. Creatinine, a byproduct of muscle metabolism, is normally released into the urine at a constant rate and its level in the urine is an indication of the urine concentration. This property of creatinine allows its measurement to be used to correct for urine concentration when measuring albumin in a random urine sample.
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.
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:
- Specialized structures in the kidney called glomeruli are composed of loops of specialized capillaries that filter the blood, allowing small substances to pass through towards the urine, but provide a barrier that keeps most large plasma proteins inside the blood vessels.
- The smaller proteins that do get through are almost entirely reabsorbed by tubes (tubules) that have a number of sections that collect the fluid and molecules that pass through the glomeruli.
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.
If a person's kidneys become damaged or diseased, 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.
How is the test used?
A urine albumin test and albumin to creatinine ratio (ACR) are used to screen for kidney disease in people with chronic conditions, such as diabetes and high blood pressure (hypertension). 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. Studies have shown that identifying individuals in the very early stages of kidney disease helps people and healthcare providers adjust treatment. Controlling diabetes and hypertension by maintaining tight glycemic control and reducing blood pressure delay or prevent the progression of kidney disease.
If albumin is detected in a urine sample collected at random, over 4 hours, or overnight, the test may be repeated and/or confirmed with urine that is collected over a 24-hour period (24-hour urine).
For urine samples collected randomly (not timed), both albumin and creatinine usually are measured and an albumin to creatinine ratio (ACR) is calculated. This is done to provide a more accurate indication of the how much albumin is being released into the urine. The American Diabetes Association has stated a preference for the ACR for screening for albuminuria indicating early kidney disease. 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.
When is it ordered?
According to the American Diabetes Association and National Kidney Foundation, everyone with type 1 diabetes should get tested starting 5 years after onset of the disease and then annually, and all those with type 2 diabetes should get tested starting at the time of diagnosis and then annually. If albumin in the urine (albuminuria) is detected, it should be confirmed by retesting twice within a 3-6 month period. People with hypertension may be tested at regular intervals, with the frequency determined by their healthcare practitioner.
What does the test result mean?
If albumin in undetectable in the urine, it is an indication that kidney function is normal.
Moderately increased albumin levels found in both initial and repeat urine tests indicate that a person is likely to have early kidney disease. Very high levels are an indication that kidney disease is present in a more severe form.
The presence of blood in the urine, a urinary tract infection, vigorous exercise, and other acute illnesses may cause a positive test result that is not related to kidney disease. Testing should be repeated after these conditions have resolved.
Is there anything I can do to prevent albuminuria (microalbuminuria)?
Yes, if you have diabetes, follow your healthcare practitioner's instructions for maintaining control over your blood glucose level. Keeping high blood pressure under control is also effective in preventing kidney damage that leads to albumin in urine (albuminuria). Some studies have shown that those who have albuminuria can prevent it from worsening or may reverse it with good glycemic control and blood pressure control, or by quitting smoking.
Are there other reasons for having increased urine albumin levels?
Yes, albumin in the urine (albuminuria) is not specific for diabetes. It may also be associated with hypertension (high blood pressure), some lipid abnormalities, and several immune disorders. Elevated results may also be caused by vigorous exercise, blood in the urine, urinary tract infection, dehydration, and some drugs.
What is the difference between serum/plasma albumin, prealbumin, and urine albumin tests?
Although the names are similar, albumin and prealbumin are completely different molecules. They are both proteins made by the liver, however, and both have been used historically to evaluate nutritional status. Serum or plasma (or blood) albumin is now more often used to screen for and help diagnose liver or kidney disease. The urine albumin test detects and measures albumin in the urine as an early indicator of kidney damage.
Is there anything else I should know?
Studies have shown that elevated levels of urinary albumin in people with diabetes or hypertension are associated with increased risk of developing cardiovascular disease (CVD). More recently, research has been focused on trying to determine if increased levels of albumin in the urine are also indicative of CVD risk in those who do not have diabetes or high blood pressure. There is currently some evidence that albuminuria is associated with an increased risk of death in adults.