Sodium - urine

Alternative names
Urinary 24 hours sodium; Urine Na+

Definition
The sodium urine test measures the amount of sodium in urine.

How the test is performed
Urine may be collected over a 24-hour period or by the “clean-catch” method. The urine is then analyzed by a laboratory.

If a 24-hour urine sample is needed, your health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test.

     
  • 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.

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, the entire penis can be placed in the bag and the adhesive attached to the skin. For females, the bag is placed over the labia. Diaper as usual over the secured bag.

This procedure may take a couple of attempts - lively infants can displace the bag, causing the specimen to be absorbed by the diaper. The infant should be checked frequently and the bag changed after the infant has urinated into the bag. The urine is drained into the container for transport to the laboratory.

Deliver it to the laboratory or your health care provider as soon as possible upon completion.

Child or adult:
Collect a “clean-catch” (midstream) urine sample. To obtain a clean-catch sample, men or boys should clean the head of the penis. Women or girls need to wash the area between the lips of the vagina with soapy water and rinse well. As you start to urinate, allow a small amount to fall into the toilet bowl to clear the urethra of contaminants. Then, put a clean container under your urine stream and catch 1 to 2 ounces of urine. Remove the container from the urine stream. Cap and mark the container and give it to the health care provider or assistant.

How to prepare for the test
No special preparation is necessary for this test, but if the collection is being taken from an infant, a couple of extra collection bags may be necessary.

The health care provider may advise you to discontinue drugs that can affect the test (see Special Considerations).

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 hydration status and the kidney’s ability to conserve or excrete sodium.

Aldosterone (see the aldosterone test), a hormone produced by the adrenal gland, plays a major role in regulating sodium levels within the body and urine. Specifically, aldosterone increases the reabsorption of sodium in the kidneys at the expense of potassium and hydrogen loss.

Reabsorption of sodium helps retain water in body tissues and the blood stream. This way, aldosterone helps maintain plasma volume and blood pressure. Dehydration and conditions that decrease kidney blood flow stimulate aldosterone production.

Normal Values
Normal values are generally 15 to 250 mEq/L/day, depending on hydration status and daily intake of dietary sodium. Normal value ranges may vary slightly among different laboratories.

Note: mEq/L/day = milliequivalents per liter per day

What abnormal results mean

Greater-than-normal urine sodium levels may indicate excessive salt intake.

Lower-than-normal urine sodium levels may indicate:

Additional conditions under which the test may be performed:

     
  • Acute tubular necrosis  
  • Hepatorenal syndrome  
  • Medullary cystic disease  
  • Glomerulonephritis  
  • Prerenal azotemia

What the risks are
There are no risks.

Special considerations
Deficient or excessive amounts of sodium in the diet may affect test results.

Drugs that can increase test measurements include some antibiotics, diuretics, prostaglandins, and certain corticosteroids.

Drugs that can decrease test measurements include NSAIDs.

Johns Hopkins patient information

Last revised: December 6, 2012
by Dave R. Roger, M.D.

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