Urine Albumin to Creatinine Ratio or ACR
Albumin is a protein that is present in large amounts in the blood. When the kidneys are working properly, only tiny amounts of albumin pass from the bloodstream into the urine. In kidney failure (the last stage of a slow process of decline in kidney function) large amounts of protein leak into the urine. A long time before this amount of damage, small changes in the blood-filtering parts of the kidney allow very small, but abnormal amounts of albumin to leak through, often as a result of having diabetes. Too little albumin is present to be detected by the usual simple urinalysis with a test strip (sometimes called a protein dipstick). This condition used to be termed microalbuminuria because of the low but significant concentration of albumin in the urine, not because it is a smaller type of the protein; however this term has been abandoned because it can be confusing. It is now simply called albuminuria.
How is the sample collected for testing?
You will be asked to collect either an early morning or random sample of urine in which albumin and creatinine will be measured by sensitive methods. The measurements are expressed as an albumin/creatinine ratio or ACR for short. The use of this ratio allows the albumin concentration to be related to the dilution of urine (as indicated by the creatinine concentration) which can depend on how much fluid you have consumed that day. ACR measurement in random urine samples has been shown to be just as good as the measurement of albumin alone in 24 hour urine samples and is much more convenient for the person being tested.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
Diabetes is a very common cause of kidney failure. Studies have shown that identifying diabetic patients who have a very early stage of kidney disease by demonstrating an abnormal ACR helps treatment to be appropriately adjusted. Good control of diabetes and other conditions, such as high blood pressure, can slow down or prevent the progression of kidney disease.
When is it requested?
What does the test result mean?
A moderately increased ACR indicates an early phase of developing kidney disease. Very high values show that kidney disease is present in a more severe form. Very low values generally indicate that kidney function is normal if other tests of kidney function, e.g. the glomerular filtration rate, also show no abnormality.
Is there anything else I should know?
Are there other reasons for having an increased urine albumin/creatinine ratio?
Yes, an increased ACR is not confined to diabetes and hypertension (high blood pressure). It may also be seen with some lipid abnormalities, urinary tract infection, several immune disorders, dehydration, certain drugs and conditions causing blood in the urine. Temporarily elevated results may also be caused by vigorous exercise.