Test Overview

A test for sodium in the urine is a 24-hour test or a one-time (spot) test that checks for how much sodium is in the urine. Sodium is both an electrolyte and a mineral. It helps keep the water (the amount of fluid inside and outside the body's cells) and electrolyte balance of the body. Sodium is also important in how nerves and muscles work.

Most of the sodium in the body is found in blood and lymph fluid. Sodium levels in the body are partly controlled by a hormone called aldosterone, which is made by the adrenal glands. Aldosterone levels tell the kidneys when to hold sodium in the body instead of passing it in the urine. Small amounts of sodium are also lost through the skin when you sweat.

Most foods have sodium naturally in them or as an ingredient in cooking. Sodium is found in table salt as sodium chloride and in baking soda as sodium bicarbonate. Many medicines and other products also have sodium in them, including laxatives, aspirin, mouthwash, and toothpaste.

Doctors may look at sodium levels in the blood and urine to see whether conditions or medicines may be causing fluid or electrolyte imbalances. Urine sodium levels are often high when blood levels are low. The urine sodium level is often low when blood levels are high. Urine sodium levels are affected by medicines and hormones. Low urine sodium levels have many causes, such as heart failure, malnutrition, and diarrhea.

Why It Is Done

A urine test to check sodium levels is done to:

• Check the water and electrolyte balance of the body.
• Find the cause of symptoms from low or high levels of sodium.
• Check the progress of diseases of the kidneys or adrenal glands.

How To Prepare

• In general, there's nothing you have to do before this test, unless your doctor tells you to.
• For 24-hour urine collection, your doctor or lab will usually give you a large container that holds about 4 litres (1 gallon).

How It Is Done

Urine sodium can be checked in a single urine sample, but it is more often measured in a 24-hour urine sample. A single urine sample (clean catch) may be taken at a health professional's office or at home. A 24-hour sample is done at home.

Timed urine collection

You collect your urine for a period of time, such as over 4 or 24 hours. Your doctor will give you a large container that holds about 4 litres (1 gallon). A small amount of preservative may be in the container. You will use the container to collect your urine.

• When you first get up, you empty your bladder.

  But don't save this urine. Write down the time you began.

• For the set period of time, collect all your urine.

  Each time you urinate during this time period, collect your urine in a small, clean container. Then pour the urine into the large container. Don't touch the inside of either container with your fingers.

• Don't get toilet paper, pubic hair, stool (feces), menstrual blood, or anything else in the urine sample.
• Keep the collected urine in the refrigerator for the collection time.
• Empty your bladder for the last time at or just before the end of the collection period.

  Add this urine to the large container. Then write down the time.

Clean-catch urine collection

1. Open the wipes. Remove the lid from the container, and set it down with the inner surface up.
2. Wash your hands before you collect the urine.
3. Clean your genitals with the provided wipes. If you have a vulva, hold the folds of skin or lips (labia) apart. Wipe the area from front to back. If you have a penis, use the wipes to clean the tip. If you have a foreskin, pull it back.
4. Start to urinate into the toilet for a few seconds. Keep holding your skin away from the urine stream.
5. After the urine has flowed for several seconds, place the collection container in the stream. Collect about 60 mL (2 fl oz).
6. Don't touch the container to your genitals.
7. Finish urinating into the toilet or urinal.
8. Carefully replace the lid on the container.
9. Wash your hands.

How It Feels

This test usually doesn't cause any pain or discomfort.

Risks

There is very little chance of having a problem from this test.

Results

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

Many conditions can affect sodium levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.