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Urine albumin-creatinine ratio
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The urine albumin-creatinine ratio is a calculation made from a urine sample. Albumin is measured, creatinine is measured, and one is divided by the other. That number estimates how much albumin is lost in the urine over 24 hours, without having to collect a whole day's worth of urine.
What it looks for makes sense if you think of the kidney as a filter. Albumin is a blood protein, and a healthy kidney does not let it pass into the urine. A damaged kidney does let some through. That is why finding albumin in the urine, called albuminuria, is a sign of kidney disease.
So why divide by creatinine? Because urine does not always come out the same: sometimes it is very dilute and sometimes very concentrated, and that alone would change the result. Creatinine is a waste product that the kidney filters and excretes in the urine, and dividing by it corrects for exactly that difference in concentration and volume. Creatinine serves as a yardstick for whether the urine came in dilute or concentrated. Even so, the ratio can vary by as much as 40 percent from one day to the next.
In brief
The urine albumin-creatinine ratio compares albumin with creatinine in a sample to estimate how much albumin is excreted in 24 hours.
A healthy kidney does not let albumin pass from the blood into the urine; a damaged one does, and finding it there is a sign of kidney disease.
Dividing by creatinine corrects for urine concentration and volume, but the ratio can vary by as much as 40 percent from day to day.
Creatinine serves as a yardstick for whether the urine came in dilute or concentrated.
Sources (2)
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of HealthAlbuminuria: Albumin in the Urine, NIDDKPublished
- National Center for Biotechnology Information, StatPearls PublishingMicroalbuminuria, StatPearlsPublished
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