Urine albumin-to-creatinine ratio (ACR)

The albumin-to-creatinine ratio compares two things in the same portion of urine: how much albumin it contains and how much creatinine. Albumin is a protein that normally stays in your blood, and healthy kidneys let almost none of it through.

The ratio is not measured separately in the laboratory. It follows from a division: your albumin value divided by your creatinine value, expressed in mg/mmol. No extra sample is needed for it.

That division does real work. Urine is dilute on one occasion and concentrated on another, and an albumin value on its own moves with it. Creatinine moves in exactly the same way, so dividing the two against each other cancels most of the dilution effect out.

Albumin in your urine is one of the earliest signals that your kidneys' filter is not closing as tightly as it should. It often shows before your eGFR changes, which is exactly why this ratio sits alongside eGFR in the guidelines.

The Dutch kidney standard calls a ratio of 3 mg/mmol or above raised. The international KDIGO guideline uses the same boundary and sorts the result into three categories: under 3, between 3 and 30, and above 30 mg/mmol.

A raised result is not a diagnosis on its own. Fever, a bladder infection, hard exercise shortly before the sample and a very high-protein meal can all push the value up temporarily. That is why an abnormal ratio is normally repeated before any conclusions are drawn. Discuss your result with your doctor or GP.

The ratio is used mainly in people at raised risk of kidney damage: with diabetes, with high blood pressure, with cardiovascular disease, and where kidney disease runs in the family.

You need two determinations in the same portion of urine for it: albumin and creatinine. If both are on your request, we add the ratio automatically.

Morning urine is preferred, because it is least affected by what you have done that day. Hard training shortly before the sample is better skipped.