Urine Albumin and Albumin/Creatinine Ratio
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The urine albumin test or albumin/creatinine ratio (ACR) is used to screen people with chronic conditions, such as diabetes and high blood pressure (hypertension) that put them at an increased risk of developing kidney disease. 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.
Albumin is a protein that is present in high concentrations in the blood. 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. (See the "What is being tested?" section for more.)
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).
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 released 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 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 in a random urine sample. 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 annually, starting 5 years after onset of the disease, and all those with type 2 diabetes should get tested annually, starting at the time of diagnosis. 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 provider.
What does the test result mean?
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. Undetectable levels are an indication that kidney function is normal.
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 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.