Urine albumin-to-creatinine ratio

What is it?

It is a urine test that measures albumin (a protein) and compares it with creatinine to find out whether the kidneys are letting an abnormal amount of protein through (MedlinePlus).

The NIDDK says albumin is a protein that may pass into the urine when the kidneys are damaged.

Other names: urine microalbumin, ACR, UACR (MedlinePlus).

Why is it done?

To screen for early kidney disease in people at higher risk: diabetes, high blood pressure, a family history of kidney disease, heart disease, age over 50, smoking, obesity (MedlinePlus).

According to MedlinePlus, because diabetes is the most common cause of kidney disease, it is important for people with diabetes to have kidney testing every year. The NIDDK states annual testing for people with type 2 diabetes or those who have had type 1 for more than 5 years.

The CDC notes that people with diabetes or high blood pressure have a higher risk of developing chronic kidney disease.

Preparation

You may be asked to avoid strenuous exercise because it may temporarily raise albumin, and to avoid meat the day before the test because it affects creatinine. Ask the provider about medicines and supplements that may affect the result (MedlinePlus).

How is it done?

A urine sample by one of three methods: a random sample at any time, an early-morning/timed sample (first urine of the morning or after 4 hours without urinating), or a 24-hour urine collection, which is the most accurate and is kept refrigerated. A "clean-catch midstream" method is requested to avoid contamination (MedlinePlus).

Understanding the result

The NIDDK states: a value of 30 mg/g or lower is within the usual range, and more than 30 mg/g may be a sign of kidney disease. The CDC notes that a urine albumin result of 30 or more may mean kidney disease. Laboratories and guidelines differ, so what counts is your laboratory's report and your doctor's interpretation.

The NHS gives ACR stages in mg/mmol as used in the UK: A1 below 3, A2 from 3 to 30, A3 above 30. The two units (mg/g and mg/mmol) are different, so do not compare one number directly with the other.

MedlinePlus says an abnormal result may indicate kidney disease if albumin is raised in two out of three tests, that larger amounts indicate more severe disease and higher cardiovascular risk, and that small amounts do not always mean disease, as they may be raised by infections, hepatitis and other conditions.

Risks and side effects

There is no known risk from giving a urine sample (MedlinePlus).

Limits of the test

Strenuous exercise, infection and inflammation may temporarily raise albumin (MedlinePlus), so the test is repeated once or twice to be sure (NIDDK and CDC).

After the test

If albumin is found in the urine, the doctor may ask for the test to be repeated once or twice to confirm (NIDDK). According to the CDC, if the albumin level stays steady or falls, it means treatment is working.

Common questions