There are a variety of tests that can be used to measure kidney function. One test is the albumin creatinine ratio (ACR). This is a urine test that’s very sensitive for detecting kidney disease.
If you have kidney disease or are at risk for it, then you may have had your ACR tested. Many people would like the albumin creatinine ratio explained, so that they can better understand what their test means. Although you may find an albumin creatinine ratio chart in the report you get from the lab, this doesn’t always happen, and many patients don’t receive an explanation of what their test results really mean.
What is the albumin creatinine ratio?
To test a patient’s albumin creatinine ratio, the levels of two different substances are tested in a single urine sample:
- Creatinine, which is a waste product normally filtered out by the kidneys. Levels of creatinine in the blood are often used as a measure of kidney function; this test measures creatinine in the urine, indicating that it has been successfully removed by the kidneys.
- Albumin, which is a protein that’s normally found in the blood. Healthy kidneys will let through only a tiny amount of albumin. When levels of albumin in the blood rise, this is a sign that the kidneys are not functioning normally.
These measurements are then used to calculate a ratio between urine albumin and creatinine. Either higher levels of albumin, or lower levels of creatinine, will result in a higher albumin to creatinine ratio.
The albumin creatinine ratio can also be called the microalbumin to creatinine ratio. These mean the same thing. The term “microalbumin” refers to the fact that very small amounts of albumin are being detected.
There is also a test called a dipstick, that looks for protein in the urine. If a urine test simply says “protein” and reports positive or negative, this generally indicates that the dipstick test was performed. This is a less sensitive test, and the ACR picks up signs of kidney damage earlier than the protein dipstick does.
What type of urine sample is used for ACR?
In the past, a 24-hour urine collection was considered the best way to conduct ACR measurement. However, studies have shown that the albumin creatinine ratio in a spot urine sample (a sample collected at a single point in time) correlates well with the albumin creatinine ratio in a 24-hour urine sample. Because of the far greater ease of collecting a single urine sample, using this method is more convenient and helps to maximize the number of patients who complete their recommended screening.
What are albumin creatinine ratio normal levels?
The ACR normal range is less than 30. At the higher end of this, the albumin creatinine ratio may be considered mildly elevated, but is not yet in a concerning range.
An albumin creatinine ratio of 30 or above, persisting for at least three months, indicates chronic kidney disease. Between 30 and 300, this is considered a moderately elevated ACR. At this level, the protein would not show up on a routine dipstick test for protein, and so that test would miss the patient’s kidney damage. However, the albumin creatinineto ratio is able to detect signs of kidney disease much earlier in the course of the disease.
An albumin creatinine ratio greater than 300 indicates severe kidney damage. This generally correlates with a significantly decreased eGFR, which is a measure of kidney function that’s determined by a blood test.
Who needs ACR measurement?
The ACR acts as a sensitive marker of kidney damage. People who are at risk for kidney disease, such as those with high blood pressure or diabetes, should have their albumin to creatinine ratio tested regularly. Because the ACR is able to detect kidney disease in its early stages, it’s useful as a screening test, so that kidney disease can be found early when it’s more treatable.
Those who already have chronic kidney disease are often also monitored using the urinary albumin to creatinine ratio, to determine whether their disease is progressing. In general, along with the ACR, the eGFR will also be measured by a blood test, to get a complete picture of how the kidneys are doing.
If you’re at risk for kidney disease, then you should strongly consider having your kidney function screened regularly to determine how your kidneys are doing. If going to a laboratory to give samples is a barrier for you, then a home test may help. You simply order a test kit online, take samples in the privacy of your own home at your convenience, and send these back to the lab. You’ll get results online within a few days, and will have the opportunity to talk with a licensed medical provider if you get a concerning result.
Sources
ACR. National Kidney Foundation. https://www.kidney.org/kidneydisease/siemens_hcp_acr. Accessed 28 June 2022.
Albumin & Creatinine - Urine. Centers for Disease Control and Prevention. https://wwwn.cdc.gov/Nchs/Nhanes/limited_access/ALCR_G_R.htm. Accessed 28 June 2022.
Gaitonde DY, Cook DL, et al. Chronic Kidney Disease: Detection and Evaluation. Am Fam Physician. 2017 Dec 15;96(12):776-783.
Microalbumin Creatinine Ratio. Medline. https://medlineplus.gov/lab-tests/microalbumin-creatinine-ratio/. Accessed 28 June 2022.
