Sodium (Na) in Urine

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

You do not need to do anything before having this test.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?).

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.

Clean-catch midstream one-time urine collection

• Wash your hands to make sure they are clean before collecting the urine.
• If the collection cup has a lid, remove it carefully and set it down with the inner surface up. Do not touch the inside of the cup with your fingers.
• Clean the area around your genitals.
  • A man should retract the foreskin, if present, and clean the head of his penis with medicated towelettes or swabs.
  • A woman should spread open the genital folds of skin with one hand. Then use her other hand to clean the area around the urethra with medicated towelettes or swabs. She should wipe the area from front to back so bacteria from the anus is not wiped across the urethra.
• Begin urinating into the toilet or urinal. A woman should hold apart the genital folds of skin while she urinates.
• After the urine has flowed for several seconds, place the collection cup into the urine stream and collect about2 fl oz (60 mL) of this "midstream" urine without stopping your flow of urine.
• Do not touch the rim of the cup to your genital area. Do not get toilet paper, pubic hair, stool (feces), menstrual blood, or anything else in the urine sample.
• Finish urinating into the toilet or urinal.
• Carefully replace and tighten the lid on the cup then return it to the lab. If you are collecting the urine at home and cannot get it to the lab in an hour, refrigerate it.

Urine collection over 24 hours

• You start collecting your urine in the morning. When you first get up, empty your bladder but do not save this urine. Write down the time that you urinated to mark the beginning of your 24-hour collection period.
• For the next 24 hours, collect all your urine. Your doctor or lab will usually provide you with a large container that holds about 1 gal (4 L). The container has a small amount of preservative in it. Urinate into a small, clean container and then pour the urine into the large container. Do not touch the inside of either container with your fingers.
• Keep the large container in the refrigerator for the 24 hours.
• Empty your bladder for the final time at or just before the end of the 24-hour period. Add this urine to the large container and record the time.
• Do not get toilet paper, pubic hair, stool (feces), menstrual blood, or other foreign matter in the urine sample.

How It Feels

There is no discomfort in collecting a one-time or 24-hour urine sample.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Taking medicines, such as birth control pills, corticosteroids, antibiotics, estrogens, tricyclic antidepressants, heparin, nonsteroidal anti-inflammatory drugs (NSAIDs), diuretics, lithium, and many medicines used to treat high blood pressure.
• Having high levels of glucose, triglycerides, or protein.
• Getting sodium in intravenous (IV) fluids given during a recent surgery or hospitalization.

What To Think About

• Sodium levels can also be measured in a blood test. To learn more, see the topic Sodium (Na) in Blood.
• To see whether the body is passing too little or too much sodium in the urine, a value called the fractional excretion of sodium (FENa) can be found by looking at the amounts of sodium and creatinine in blood and urine. In a person with kidney failure, a low FENa may mean less blood flow to the kidneys is causing the kidney failure.