What is Creatinine Urine - Spot Sample?
Also Known As:
ACR, UACR, Albumin-Creatinine Ratio, Microalbumin-Creatinine Ratio, Microalbumin Test, Urine Dipstick, Albuminuria Test, Proteinuria Test
Albumin is a protein that is normally found in the blood, and ordinarily, the kidneys prevent most albumin from entering urine.
A urine albumin test checks the levels of albumin in the urine because abnormal amounts of this protein can be a sign of kidney problems. Several methods exist for measuring urine albumin including a urine dipstick, a one-time urine sample that compares the ratio of albumin to creatinine, and a 24-hour urine collection.
Urine albumin tests are often used for screening and diagnosis of kidney disease. They can also help track the progression of disease and how well the kidneys respond to treatment.
The purpose of a urine albumin test is to determine if there is an abnormal amount of the protein albumin in a urine sample.
Excess albumin on this type of test indicates that too much of this protein has passed from the blood to the urine, which can reflect a problem with the kidneys. Different types of urine albumin tests can be used for diagnosis, screening, and monitoring of kidney disease.
Diagnosis includes medical exams or tests that are done after symptoms have appeared. A urine albumin test may be included in the diagnostic process if you notice health changes that could be caused by kidney problems.
Examples of symptoms that can be related to kidney impairment include urinary irregularities such as frothy urine, blood in the urine, or changes in urine volume or frequency. Abnormal swelling, itching, loss of appetite, and fatigue can also occur as a result of kidney problems.
Screening tests are designed to try to find health problems before symptoms occur with the goal of enabling treatment before a disease has significantly progressed. Because the early stages of kidney disease may not cause symptoms, urine albumin tests are often used to look for indications of kidney problems.
A urine albumin-to-creatinine ratio test is a common way to screen for high levels of albumin, which is known as albuminuria. This screening is most often done in people who have a higher risk of kidney disease including people with diabetes, high blood pressure, or a family history of kidney problems. Screening may also be recommended in older adults and people in some racial and ethinc groups.
Screening for kidney disease may combine a urine albumin test with another kidney function test, known as an estimated glomerular filtration rate (eGFR) test, that assesses how well the kidneys are filtering the blood.
The presence of moderate or severely increased levels of albumin in the blood has also been associated with cardiovascular disease, obesity, and diabetes, so screening with urine albumin tests may provide information about risks related to these conditions and their potential complications.
Another use of urine albumin tests is for monitoring kidney health over time. This often means using repeat urine albumin tests at regular intervals to check how kidney disease is progressing or to see how well treatments are working.
What does the test measure?
A urine albumin test is a measurement of the protein albumin. Albumin is a common protein in the blood that helps keep fluid from leaking out of blood vessels. Albumin also helps carry substances, including enzymes and vitamins, through the body.
While albumin is supposed to be found in the blood, very little albumin should enter the urine if the kidneys are functioning properly. Different types of urine albumin tests are designed to detect albumin in the urine:
- A urine dipstick test is a test in which a test strip turns a different color based on the amount of albumin in the sample.
- A 24-hour urine sample requires collecting all of your urine for a full day. The laboratory then measures the total amount of albumin in that complete sample.
- An albumin-to-creatinine ratio test measures both albumin and creatinine in a one-time sample, also known as a spot urine sample. Creatinine is a chemical byproduct of normal muscle activity, and it is normally removed from the body in urine. Total daily creatinine production is relatively consistent, so an albumin-to-creatinine ratio test is a way to estimate your total daily urine albumin level without having to do a full 24-hour urine sample.
A dipstick test does not provide an exact measurement of albumin.
A 24-hour urine sample provides an albumin measurement that is typically listed as milligrams per 24 hours (mg/24 hours).
An albumin-to-creatinine ratio test is reported in milligrams of albumin per gram of creatine (mg/g) found in one deciliter of urine. This may also be listed in international units, which are measured in milligrams per millimole (mg/mmol).
Some laboratories or health professionals may report urine albumin test results using an estimated albumin excretion rate (eAER). The eAER is a calculation with a formula that incorporates the albumin-to-creatinine ratio with the ability to adjust the expected daily creatinine level based on individual factors such as body composition, age, sex, and race. While not broadly used, the eAER may be most beneficial for patients with abnormal daily production of creatinine.
When should I get a urine albumin or albumin-to-creatinine ratio test?
Urine albumin tests can be used in several different medical contexts.
For diagnosis, they are generally performed if you have signs of possible kidney impairment. Urinary changes, swelling, and unexplained itching are examples of symptoms that can be associated with kidney problems. In these cases, a urine albumin test may be performed along with other kidney function tests.
Screening with a urine albumin test is only recommended for some people. For people without risk factors for kidney disease, the downsides of this testing, including financial costs and potential unnecessary follow-up, are considered to be greater than the potential benefits. As such, this screening is not recommended in the population in general.
Instead, screening is usually reserved for people who are at a higher risk of having kidney problems. Urine albumin testing is recommended for people with diabetes, and this testing may be done every year for people with type 2 diabetes.
Screening is also advised in people with one or more of the following risk factors for kidney disease:
- High blood pressure
- A family history of chronic kidney disease
- Cigarette smoking
- Cardiovascular disease
- Belonging to certain racial or ethnic groups
If you have had an abnormal albumin level in your urine or have been diagnosed with kidney disease in the past, you may have repeat testing to monitor your urine albumin levels. In these cases, the doctor may request 24-hour urine samples to more precisely measure the amount of albumin.
How to get tested
Testing for urine albumin levels is normally ordered by a doctor. Your doctor can recommend either a dipstick, single urine sample, or 24-hour urine collection based on your health situation including whether you have any symptoms or risk factors for kidney disease.
Dipstick tests may be performed in a doctor’s office, health clinic, or hospital. Spot urine samples can also be collected in these medical settings. A 24-hour urine sample involves collecting all your urine in special containers over the course of a full day.
Dipstick tests are a kind of point-of-care test, which means they provide results on-site and without having to send the sample to a lab. Point-of-care devices exist for measuring albumin in a spot urine sample, but these devices are not widely available. Most spot urine samples and virtually all 24-hour urine collections are analyzed by a laboratory.
Can I take the test at home?
Some types of urine albumin tests can be taken at home. At-home test kits generally fall into two categories:
- Self-test kits: Self-test kits allow you to take and analyze the sample at home. These kits are dipstick tests in which a special paper or test strip is dipped into a cup of urine that you have collected. The test strip changes color based on the amount of albumin detected.
- Self-collection kits: This type of test involves obtaining your test sample at home and then sending it to a laboratory for analysis. Almost all 24-hour urine samples require self-collection with special bags or containers provided by your doctor.
Urine albumin-to-creatinine ratio testing is not normally done at home.
There are benefits and drawbacks to each kind of urine albumin testing, so it is important to talk with your doctor about which type of test is most appropriate in your situation and whether it can be performed at home.