Urine Albumin to Creatinine Ratio Calculator
Turn a urine albumin and a urine creatinine into the ratio that decides the albuminuria category and the daily loss.
What it does
Leaking albumin in the urine is the earliest sign that the kidneys are in trouble, and for a long time the way to measure it was to collect every drop of urine for a day and weigh what was in it. That is awkward, and it is not what anybody does now.
The National Institute of Diabetes and Digestive and Kidney Diseases explains the modern replacement. A urine albumin to creatinine ratio on a spot sample is the recommended test, and it is a ratio between two measured substances: the urine albumin in milligrams per decilitre divided by the urine creatinine in grams per decilitre, which gives the ratio in milligrams per gram. The reason it works is that the creatinine corrects for variation in urine concentration, something a dipstick cannot do.
The same source notes that the ratio is about equal to the albumin excretion in milligrams per day, that a first morning void is preferred because the urine is more concentrated, and that a random sample is acceptable when a morning sample is not available. It also says that a 24 hour collection is not needed for routine assessment.
The KDIGO guideline turns the number into a category, because that is what the risk tables are built on. Anything under 30 mg per gram is A1, normal to mildly increased, 30 to 300 is A2, moderately increased, and above 300 is A3, severely increased. The guideline lists the same three bands for the older 24 hour measurement.
The limits are worth stating. The ratio is a screening number and it changes with exercise, with a fever and with a urinary infection, so a raised result is usually repeated before it means anything. And it does not replace the other checks, because a person can have a normal ratio and still have reduced kidney function.
How to use
- Enter the urine albumin in milligrams per decilitre, from the laboratory report.
- Enter the urine creatinine in milligrams per decilitre, from the same report.
- Read the ratio in milligrams per gram, which is the number used in the guidelines.
- Read the category, which is where the risk tables are indexed.
- Read the estimated daily albumin excretion, which is roughly the same number in different units.
- Take a raised result to your clinician, who will usually ask for it to be repeated, and look at it alongside the filtration rate and the blood pressure.
Formula
- ACR
- Albumin to creatinine ratio, in milligrams of albumin per gram of creatinine.
- Albumin
- Urine albumin concentration, in milligrams per decilitre.
- Creatinine
- Urine creatinine concentration, in milligrams per decilitre.
The SI form of the ratio is in milligrams per millimole, and the KDIGO conversion factor between the two is 0.113. The category boundaries are the same in both: under 3, 3 to 30, and over 30 milligrams per millimole.
Worked example
Example: urine albumin of 15 mg per dL and urine creatinine of 100 mg per dL
Defaults: a urine albumin of 15 mg per dL and a urine creatinine of 100 mg per dL.
- The creatinine in grams per decilitre is 100 divided by 1000 = 0.1 g per dL.
- The ratio is the albumin divided by that, 15 over 0.1 = 150.00 mg per g.
- The same ratio in SI units is 150 x 0.113 = 16.950 mg per mmol.
- The estimated albumin excretion is about the same number, 150 mg per day.
- The KDIGO bands are 30 and 300 mg per g, and 150 sits between them, so the category is A2.
- The plain ratio of the two measurements is 15 over 100 = 0.15, which is the number the laboratory often prints.
- The tool shows 150.00 mg per g, 16.950 mg per mmol, A2 moderately increased, 150 mg per day and 0.15.
Reference table
| Ratio in mg per g | Ratio in mg per mmol | Category | KDIGO description |
|---|---|---|---|
| 5 mg per g | 0.565 mg per mmol | A1 | normal to mildly increased |
| 30 mg per g | 3.390 mg per mmol | A2 | moderately increased |
| 150 mg per g | 16.950 mg per mmol | A2 | moderately increased |
| 300 mg per g | 33.900 mg per mmol | A3 | severely increased |
Limits
- The ratio changes with exercise, with a fever and with a urinary infection, so a raised result is normally repeated.
- It is a screening number and it does not replace the measurement of the filtration rate.
- A very dilute or very concentrated sample can make the result unreliable, and the creatinine itself has to be in a sensible range.
- It says nothing about the cause, so diabetes, high blood pressure and glomerular disease all look the same on this test.
Common mistakes
- Mixing up the units of the creatinine. The NIDDK formula uses grams per decilitre, and putting milligrams per decilitre in that slot makes the answer a thousand times too small.
- Forgetting that the same urine has to be used for both measurements, or the correction for dilution is meaningless.
- Reading the A2 band as mild. It is moderately increased, and it is the band that most often leads to a change in treatment.
- Using a 24 hour excretion and a spot ratio in the same table, which are two different measurements of the same thing.
- Expecting a single raised result to be the answer, when the guideline says the finding has to be persistent.
Try it yourself
Quick checks. Answers sit tucked under each question.
What category does a ratio of 45 mg per g fall in?
A2, moderately increased, because the A1 band stops at 30 mg per g. The same ratio in SI units is 45 x 0.113 = 5.085 mg per mmol, and the boundary there is 3 mg per mmol.
What if the urine is more dilute, with the creatinine at 40 mg per dL?
The ratio doubles, because the correction for dilution divides by the creatinine. With the same albumin of 15 mg per dL the ratio becomes 375.00 mg per g, which moves it into A3, severely increased. That is the whole point of the ratio, and it is why a dilute sample with a high albumin needs a repeat.
How much albumin is being lost in the example?
About 150 mg per day, which is the NIDDK rule that the ratio in milligrams per gram is roughly equal to the albumin excretion in milligrams per day. It is an estimate rather than a measurement, and it is the reason a 24 hour collection is no longer needed for routine checks.
Questions
What is the albumin to creatinine ratio?
A ratio between the urine albumin and the urine creatinine that corrects the albumin for how dilute the urine is. The NIDDK describes it as the recommended test for assessing and monitoring urine albumin.
Why use a ratio instead of a dipstick?
Because a dipstick reads concentration, which changes with how much water the kidneys made, so it can miss a real loss of albumin in dilute urine or over-read it in concentrated urine. The NIDDK says the ratio corrects for that variation in urine concentration.
What are the A1, A2 and A3 categories?
The albuminuria bands of the KDIGO guideline. A1 is under 30 mg per g, normal to mildly increased, A2 is 30 to 300, moderately increased, and A3 is above 300, severely increased.
Do I need a 24 hour urine collection?
No, not for routine assessment. The NIDDK says a 24 hour collection is not necessary, and that a first morning void is preferred while a random sample is acceptable.
What if the ratio is raised?
It has to be repeated, because exercise, fever and a urinary infection can all push it up for a day. Your clinician will also look at the filtration rate, the blood pressure and the other urine tests.
Does the ratio replace the other kidney tests?
No. The KDIGO classification of chronic kidney disease uses two dimensions, the filtration rate and the albuminuria category, and a person can have a normal ratio and still have reduced filtration.
Sources
- National Institute of Diabetes and Digestive and Kidney Diseases: assess urine albumin, with the ratio formula
- KDIGO 2024 clinical practice guideline for chronic kidney disease, with the albuminuria categories