ACR most commonly stands for albumin-creatinine ratio, a simple urine test that checks how well your kidneys are working. It measures two substances in your urine: albumin (a protein that should stay in your blood) and creatinine (a waste product your muscles naturally produce). The ratio between them reveals whether your kidneys are leaking protein, one of the earliest signs of kidney damage.
ACR can also refer to the American College of Radiology or the American College of Rheumatology, two major medical organizations. But if you’ve been told you need an ACR test or saw it on lab results, it’s almost certainly the urine albumin-creatinine ratio.
How the ACR Test Works
Healthy kidneys act as precise filters. They keep useful proteins like albumin circulating in your bloodstream while removing waste products like creatinine so they leave your body through urine. When the kidneys are damaged, those filters start to break down. Albumin slips through into your urine, while creatinine may not be cleared as efficiently.
The ACR test captures this by comparing the amount of albumin to the amount of creatinine in a single urine sample. Using a ratio rather than just measuring albumin alone accounts for how concentrated or dilute your urine happens to be at the time, giving a more reliable picture.
What the Numbers Mean
ACR results are reported in milligrams per gram (mg/g). The thresholds are straightforward:
- Below 30 mg/g: Normal. Your kidneys are filtering properly.
- 30 to 299 mg/g: Moderately increased albumin in urine. This stage, sometimes called microalbuminuria, signals early kidney damage.
- 300 mg/g or higher: Severely increased. This indicates more advanced kidney damage that needs prompt attention.
International guidelines use the labels A1, A2, and A3 to classify these same ranges. A1 is normal, A2 is moderately increased, and A3 is severely increased. If you see these categories on a lab report, they correspond directly to the numbers above.
Why Your Doctor Ordered This Test
ACR testing is standard screening for people with diabetes or high blood pressure, the two leading causes of chronic kidney disease. These conditions damage the tiny blood vessels inside the kidneys over time, and albumin leaking into the urine is often the first detectable sign, sometimes appearing years before you’d notice any symptoms.
The test is also used to monitor people already diagnosed with kidney disease. Tracking changes in your ACR over time helps determine whether treatment is working or whether the disease is progressing. According to the National Kidney Foundation, albumin can show up in urine even when your overall kidney filtration rate still looks normal, which is why the ACR catches problems that other tests might miss.
ACR and eGFR: Two Pieces of One Puzzle
You’ll often see ACR results paired with another number called eGFR (estimated glomerular filtration rate). These tests measure different things. The ACR detects kidney damage by looking for protein leaking into urine. The eGFR measures kidney function by estimating how efficiently your kidneys filter blood, using a simple blood draw.
You need both to get the full picture. It’s possible to have a normal eGFR (above 60) but an elevated ACR, meaning there’s damage even though your kidneys are still compensating. The reverse is also true: your ACR can be normal while your eGFR is low, indicating reduced function without significant protein leakage. Either abnormality on its own can signal chronic kidney disease.
What an Elevated ACR Tells You Beyond the Kidneys
An ACR above 30 mg/g doesn’t just flag kidney problems. It’s also a marker of broader cardiovascular risk. When albumin leaks through the kidney’s filters, it reflects damage to small blood vessels throughout the body, not just in the kidneys. Research published in BMC Cardiovascular Disorders found that people with heart disease and elevated ACR levels had roughly two to three times the risk of dying from cardiovascular causes compared to those with low ACR levels. This held true regardless of whether they had diabetes.
Even modest elevations within the “normal” range appear to carry meaning. The same study found that rising ACR levels still increased the risk of death by about 1.5 times among heart disease patients, even when results stayed below the 30 mg/g threshold. This is why some providers pay attention to the trend in your numbers, not just whether you’ve crossed a cutoff.
How the Test Is Done
The ACR requires only a single urine sample, typically collected first thing in the morning when your urine is most concentrated. There’s no need for a 24-hour urine collection, which used to be the standard approach. Research comparing the two methods found that a spot urine sample performs just as well for predicting kidney outcomes and is far more practical.
No fasting or special preparation is needed. You simply urinate into a cup, and the lab runs the analysis. Results are usually available within a day or two.
What Can Skew Your Results
A few things can temporarily push albumin into your urine without meaning your kidneys are damaged. Strenuous exercise, fever, urinary tract infections, and dehydration can all cause a false elevation. Menstruation can also affect results. For this reason, a single elevated ACR reading is typically confirmed with a repeat test. A diagnosis of chronic kidney disease requires abnormal results lasting at least three months.
Muscle mass also matters. Because creatinine comes from muscle breakdown, people with very high or very low muscle mass may see slightly skewed ratios. Your provider can factor this in when interpreting your results.
How Often to Get Tested
If you have diabetes or high blood pressure, annual ACR screening is the standard recommendation. The CDC emphasizes that regular kidney testing gives you the best chance of catching chronic kidney disease early, when treatment is most effective at slowing progression. If your ACR is already elevated, your provider will likely check it more frequently to monitor how you’re responding to treatment, whether that involves blood pressure control, blood sugar management, or other interventions targeting kidney protection.