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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 (about 85%) 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.
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 L (1 gal). 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
- Wash your hands before you collect the urine.
- Prepare the container.
If the container has a lid, remove the lid and set it down with the inner surface up.
- Clean the area around your penis or vagina.
- Start to urinate into the toilet or urinal.
- Collect the urine in the container.
After the urine has flowed for several seconds, place the collection container in the stream. Collect about 60 mL (2 fl oz) of this "midstream" urine without stopping the flow. Don't touch the rim of the container to your genital area.
- Finish urinating.
- Replace the lid on the container.
- Wash your hands.
How It Feels
This test usually doesn't cause any pain or discomfort.
There is very little chance of having a problem from this test.
Results are ready in 1 day.
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.
Current as of: September 8, 2022
Author: Healthwise Staff
Adam Husney MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Martin J. Gabica MD - Family Medicine
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