Albumin-to-Creatinine Ratio (ACR)

Your kidneys are two organs on either side of your spine near your waist. Filters in your kidneys remove waste and extra water from your blood and get rid of them through urine. Albumin, however, is not a waste product. It is a common protein found in blood. Therefore, very little, if any, of it should pass into your urine.

In healthy kidneys, only a trace of albumin, at most, will get through the filters. This trace is often called microalbumin. But if your kidneys are damaged, large amounts of albumin may pass into your urine.

Creatinine, however, often appears in your urine. It is a waste product that comes from daily wear and tear on your muscles. Your kidneys usually get rid of this protein at a steady rate. The microalbumin creatinine ratio test compares the levels of albumin in your urine to your levels of creatinine. This ratio can help your health care provider tell if your body is getting rid of albumin at an increased rate, and it is especially useful for picking up kidney damage at an early stage and for guiding the management and outlook of long-term kidney disease.

If your microalbumin creatinine ratio shows an abnormal amount of albumin in your urine, you will likely need more tests to confirm your results. That's because temporary increases in albumin levels may be caused by exercise, certain medicines, fever, and inflammation in the body.

In current kidney disease guidelines (KDIGO), a urine albumin-to-creatinine ratio under 30 mg/g is considered normal to mildly increased. A ratio of 30 to 300 mg/g is called moderately increased albuminuria and is often the first sign of kidney damage, especially in people with diabetes. A ratio above 300 mg/g is considered severely increased and points to more advanced kidney damage. The same thresholds are used for males and females.

Usually, you'll have one or two more tests during the three to six months after your first test. If two out of three tests show high albumin, that points to early kidney disease and is a reason to step up blood pressure and blood sugar control and consider medicines that protect the kidneys.

Higher or rising amounts of albumin in your urine usually mean more serious kidney disease that's likely to progress faster, and a higher risk for problems with your heart and blood vessels (vascular diseases).

Smaller amounts of albumin in your urine don't always mean kidney disease. Other conditions that cause inflammation may increase albumin in urine, including urinary tract infections, gum infections (periodontitis), and hepatitis. Your test results may also be affected by your muscle density and your diet, age, and race.