• 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.

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.

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

Lower-than-normal urine sodium levels may indicate:

• Aldosteronism
• Congestive heart failure
• Diarrhea and dehydration status
• Renal failure

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