This test may be done using a random urine sample or a 24-hour urine collection.
If a 24-hour urine sample is needed:
On day 1, urinate into the toilet when you get up in the morning.
Afterwards, collect all urine in a special container for the next 24 hours.
On day 2, urinate into the container when you get up in the morning.
Cap the container. Keep it in the refrigerator or a cool place during the collection period.
Label the container with your name, the date, the time of completion, and return it as instructed.
For an infant, thoroughly wash the area around the urethra. Open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on the infant. For males, place the entire penis in the bag and attach the adhesive to the skin. For females, place the bag over the labia. Diaper as usual over the secured bag.
This procedure may take a couple of attempts -- lively infants can move the bag, causing the urine to be absorbed by the diaper. Check the infant frequently and change the bag after the infant has urinated into it. Drain the urine from the bag into the container provided by your health care provider.
Deliver it to the laboratory or your health care provider as soon as possible upon completion.
How to prepare for the test
Your health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test.
Drugs that can increase test measurements include:
Drugs that can decrease test measurements include:
Nonsteroidal anti-inflammatory drugs (NSAIDs)
If a 24-hour urine collection is being taken from an infant, a couple of extra collection bags may be necessary.
How the test will feel
The test involves only normal urination, and there is no discomfort.
Why the test is performed
The test is often used to determine your hydration status and your kidney's ability to conserve or remove sodium from the urine.
Additional conditions under which the test may be performed:
Normal values are generally 40 to 220 milliequivalents per liter per day (mEq/L/day), depending on how much fluid and salt you consume.
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
Greater than normal urine sodium levels may be caused by:
Too much salt in the diet
Certain medications, such as diuretics
Adrenal gland insufficiency
Lower than normal urine sodium levels may be a sign of:
Landry DW, Bazari H. Approach to the patient with renal disease. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 116.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.