Sodium, urine

Alternative names:

urinary 24 hours sodium; urine Na+

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.

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

• On day 1, urinate into the toilet upon arising in the morning.
• Collect all subsequent urine (in a special container) for the next 24-hours.
• On day 2, urinate into the container in the morning upon arising.
• 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 your 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. Place a diaper over the infant (bag and all). The infant should be checked frequently and the bag changed after the infant has urinated into the bag. For active infants, this procedure may take a couple of attempts--lively infants can displace the bag, causing an inability to obtain the specimen. 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 wipe 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 (this clears the urethra of contaminants). Then, in a clean container, catch about 1 to 2 ounces of urine and remove the container from the urine stream. Give the container 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:

This test may be performed to indirectly indicate the function of the adrenal cortex or to detect or monitor conditions that result in abnormal urine sodium levels.

Aldosterone (for more information see the aldosterone test) is a hormone (produced by the adrenal cortex) that plays a major role in regulating sodium levels within the body. Aldosterone increases the reabsorption of sodium in the kidneys. The level of aldosterone in the plasma is indirectly controlled by the amount of sodium in plasma. Renin is an enzyme released by the juxtaglomerular cells of the kidney into the blood in response to sodium depletion and/or low blood volume. Renin converts angiotensinogen (a protein secreted into the blood by the liver) to angiotensin I. Angiotensin I is converted to angiotensin II by an enzyme in the veins of the lungs. Angiotensin II acts on the adrenal cortex to stimulate the release of aldosterone. Aldosterone increases reabsorption of sodium and excretion of potassium in the distal tubules of the kidneys. Reabsorption of sodium is accompanied by reabsorption of water, which raises blood pressure.