Urine microalbumin (ACR): early kidney damage screening explained

Albumin is the main protein in blood. Healthy kidneys filter blood while keeping albumin in; when the filters are damaged, small amounts leak into urine. Older terminology called a small leak microalbuminuria, and the laboratory test was called urine microalbumin. Lab Tests Online UK explains the modern test is the urine albumin to creatinine ratio, ACR, which relates the albumin concentration to the creatinine concentration so that dilute and concentrated urine can be compared fairly.

The same source says ACR on a random urine sample has been shown to be just as good as measuring albumin alone in a 24-hour collection, and much more convenient. Urine protein, by contrast, is measured on a dipstick when albumin levels are high enough.

Diabetes is a very common cause of kidney failure, and the earliest stage of kidney disease in diabetes can be seen as an abnormal ACR before the usual kidney blood tests change. Lab Tests Online UK says ACR should be requested when diabetes is first diagnosed and then usually annually, or more often if significantly raised values are found, and that it is also used annually in people with high blood pressure. Identifying the early stage helps treatment to be adjusted appropriately, and good control of diabetes and other conditions such as high blood pressure can slow down or prevent the progression of kidney disease.

The NHS says there are usually no symptoms in the early stages of chronic kidney disease and that it may only be found when blood or urine tests are done for another reason, so regular tests are advised for people at high risk such as those with diabetes or high blood pressure.

You are asked to give an early morning or random urine sample, in a clean container. No special preparation is needed, but tell the clinician if you have a fever, a urinary tract infection or have exercised vigorously in the previous day, because these can raise the result temporarily. If the first test is raised, it is usually repeated, because other causes may be temporary.

A moderately increased ACR indicates an early phase of developing kidney disease, very high values show more severe kidney disease, and very low values generally indicate normal kidney function if other tests such as the glomerular filtration rate are also normal, according to Lab Tests Online UK. Your laboratory report prints the cut-offs used. Because ACR can fluctuate, doctors generally want more than one raised result over a few months before concluding persistent albuminuria.

The NICE approach summarised by the same source combines ACR with eGFR to categorise kidney function and guide care, giving a fuller picture than either alone.

Recent studies have shown that in people with type 2 diabetes an abnormal ACR indicates an increased risk of developing heart and blood vessel disease. That is why a raised result prompts attention to blood pressure, cholesterol, smoking and glucose as well as the kidneys. The NHS notes that even mild chronic kidney disease increases the risk of cardiovascular disease.

A raised ACR leads to a repeat test and a review of blood pressure, glucose control, kidney blood tests and medicines. Treatment may include blood pressure medicines that protect the kidneys, better diabetes control and lifestyle measures; the NHS says medicines can help the kidneys keep working for longer. See a GP promptly for swollen ankles, foamy or blood-stained urine or persistent tiredness.