The urine 24-hour volume test is used to measure the amount of urine your body produces in a day. This is a noninvasive procedure that involves no pain or discomfort. This simple test is typically used to help diagnose problems with kidney function.
Your doctor may order this test if he or she suspects a kidney disease or if you are producing abnormally large volumes of urine (a condition called polyuria), as seen in diabetes insipidus, an uncommon condition that occurs when the kidneys are unable to conserve water.
Urine volume is also measured as part of the creatinine clearance test or any other test used to measure the amount of a substance eliminated in a 24-hour period.
This test may be performed alone or in conjunction with other procedures to help the doctor decide if you have kidney disease.
There is very little preparation needed for the urine 24-hour volume test. Depending on your current medical condition and/or the reasons for the test, your doctor may give you more specific instructions.
Tell your doctor if you are pregnant or think you may be pregnant. Be sure to inform your doctor about any current prescription and over-the-counter medications and supplements you are taking and ask if any of these will interfere with the results.
Typically, no fasting or preparatory medications are required. However, based on the reasons for the test, your doctor may advise you to avoid certain foods or beverages during the test.
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 are at home or not on the go. Ask if you must begin the test at a particular time, and adjust your schedule accordingly.
You will be given one or more containers for collecting and storing urine. Make sure you understand when and where you should return the container or containers.
The goal is to collect your urine output for a 24-hour period. This can be done in the hospital if you are a patient, but it is easily done on an outpatient basis. The test should begin at a specific time and end at the same time on the following day. The test will follow these steps:
- Your test will usually begin in the morning. On the first day, do not collect your first morning urine, but note and record the time.
- Collect all your urine for the next 24 hours, keeping the storage container refrigerated.
- Collect your first morning urine on the second day at the same time you began the test yesterday.
- Keep the container cool until it is time to return it. Make sure the cover on the container is tight and return it promptly to the lab or doctor’s office as instructed.
- Under some circumstances, your doctor may want you to repeat the procedure several times.
If your baby’s urine is being collected, you will be given special urine collection bags with adhesive paper to keep them in place. Follow these steps:
- Wash the area around the urethra.
- Place the urine collection bag on the baby. For boys, place the entire penis in the bag. For girls, place the bag over the labia. You may place a diaper over the bag.
- Check the bag frequently, draining urine from the bag into the urine collection container. Replace with a clean bag.
- Keep the collection container refrigerated until it is time to return it.
- After the 24-hour period is complete, return the container as instructed by your health care provider.
To achieve accurate results, it is important that you follow instructions. The accuracy of your test could be compromised by several factors, including:
- failing to collect all your urine in the 24-hour period
- going beyond the 24-hour period and collecting too much urine
- spilling urine from the container
- not keeping the urine cool
- not returning the urine sample promptly
Other factors that may interfere with results include acute stress and vigorous exercise, so inform your doctor if that is the case. In some of these circumstances, your doctor may want you to repeat the test.
The urine 24-hour volume test is noninvasive, involving only routine urination, so there are no side effects or risks.
The normal range of urine output is 800 to 2,000 milliliters per day if you have a normal fluid intake of about two liters per day. However, different laboratories may use slightly different values. Your doctor will explain what your particular numbers mean.
Normal urine is sterile and contains no bacteria, viruses, or fungi. Urine is a mixture of water and chemicals such as sodium, potassium, urea (formed when protein breaks down), and creatinine (formed when muscles breakdown), along with other chemical compounds. If your urine contains too much or too little of these chemicals, or if your output is unusually high or low, your doctor may want to order additional testing.
Abnormally low urine volume may indicate inadequate fluid intake, dehydration, or renal insufficiency or failure.
Abnormally high urine volume may indicate diabetes, diabetes insipidus—renal, diabetes insipidus—central, and some forms of kidney failure. High volume may also result from unusually large fluid intake or the use of diuretic medications.
Your doctor will explain the results of your test and advise if additional testing is required.