Creatinine is a chemical waste product produced by muscle metabolism. When your kidneys are functioning normally, they filter creatinine and other waste products out of your blood. These waste products are removed from your body through urination.
A creatinine urine test measures the amount of creatinine in your urine. The test can help your doctor evaluate how well your kidneys are functioning. This is useful for diagnosing or ruling out kidney disease and other conditions affecting the kidneys.
Your doctor may use a random urine sample to test for creatinine. However, they’ll order a urine 24-hour volume test in most cases. Although one sample of urine can be tested for creatinine, it is more accurate to collect the urine for a whole day to get that value. The creatinine in your urine can vary a lot based on diet, exercise, and hydration levels, so a spot check is not as helpful. As the name suggests, this creatinine urine test measures the amount of urine produced in a day. It isn’t a painful test, and there aren’t any risks associated with it.
The 24-hour volume test is noninvasive and involves only the collection of urine. You’ll be given one or more containers for collecting and storing urine. Since this test involves collecting and storing urine for a 24-hour period, you may want to consider scheduling the test for a day when you’re at home.
Before the test, you should do the following:
- Tell your doctor if you’re pregnant or think you may be pregnant.
- Tell your doctor about any supplements or prescription and over-the-counter medications you’re taking. Some supplements and drugs can interfere with the test results. Your doctor can tell you which ones to avoid.
- Avoid certain foods or beverages if your doctor advises you to do so.
- Ask your doctor if you need to begin the test at a particular time of day.
- Make sure you understand when and where you should return the container of urine.
To perform the test, you’ll use a special container to collect your urine for the next 24 hours. Ask your doctor how to collect urine if you’re unsure how to do so. Failure to follow instructions could lead to false results, which means you may have to repeat the test.
The test should begin at a specific time and end at the same time on the following day.
- On the first day, don’t collect the urine from your first time urinating. However, make sure you note and record the time. This will be the start time of the 24-hour volume test.
- Collect all your urine for the next 24 hours. Keep the storage container refrigerated throughout the process.
- On the second day, try to urinate around the same time that the test started on the first day.
- When the 24-hour period is over, cap the container and promptly return it to the lab or doctor’s office as instructed.
- Be sure to tell your doctor if you were unable to follow all the instructions. You should report any missed urine, spilled urine, or urine collected after the 24-hour time period ended. You should also tell them if you were unable to store the container of urine in a cool place.
There are natural variations in creatinine output due to age and body mass. The more muscular you are, the higher your range will be. It’s also important to note that not all laboratories use the same values. Results are dependent on the proper collection of your urine sample.
Normal urine creatinine values generally range from 74.3 to 107 micromoles per liter (mcmol/L), according to the Mayo Clinic. Creatinine values that fall outside the normal range may be an indication of:
- kidney disease
- kidney infection
- kidney failure
- urinary tract obstruction, such as kidney stones
- late-stage muscular dystrophy, which is a group of diseases that damage and weaken your muscles over time
- myasthenia gravis, which is an autoimmune disease that causes muscle weakness
Abnormal values can also occur in people who have diabetes or a diet that’s high in meat or other proteins.
It’s very difficult to evaluate the test results on your own. You should discuss your results with your doctor.
Depending on your results, your doctor may order a serum creatinine test. This is a type of blood test that measures the amount of creatinine in your blood. Your doctor may use it to help confirm a diagnosis.