A urine sodium test checks the amount of sodium in a sample of your pee to see whether it’s at a normal level.
Having too much or too little sodium can mean there’s an issue with your kidneys or perhaps another health matter. They may be asked to take a urine sodium test after you’ve already taken a sodium blood test and gotten results that are not normal.
Sodium is an important electrolyte (a mineral in your blood and other bodily fluids) that helps your body and cells function. It helps your body regulate how much fluid it retains.
Sodium is in almost everything you eat -- from chips and bread to even some medicine. When you eat too much sodium, your kidneys have the job of clearing it from your body. But if your kidneys are damaged, the organs can’t remove sodium efficiently.
The urine sodium test helps to figure out whether your kidneys are working as they should to remove sodium.
Who Needs This Test?
Your doctor may order the urine sodium test after you’ve gotten abnormal results on a sodium blood test, which can point to acute kidney failure. The test helps distinguish between two common causes of kidney failure -- pre-renal (dehydration) and tubular death (ATN). They are treated differently.
You could also get this test if you’ve started a new treatment and your doctor wants to see how well it is working.
How Do I Prepare for the Test?
The urine sodium test poses no risks.
Before your test, you should tell your doctor what medicine and supplements you’re taking. Some drugs could affect your test results, so they may ask you to stop taking certain ones before giving a urine sample. These include:
Nonsteroidal anti-inflammatory drugs (NSAIDs). These medications are used to reduce inflammation and include aspirin (Bayer, Bufferin, Excedrin), ibuprofen (Motrin, Advil), and Naproxen sodium (Aleve).
Before the test, you may be asked to drink a certain amount of water. But this depends on your doctor. Depending on your instructions, you may not need to prepare anything before the test.
What Happens During the Test
You’ll pee into a container, typically in your doctor's office, and it will be taken to a lab. The lab will analyze the sample and let you know whether there was a normal amount of sodium in your urine.
Depending on what your doctor suggests, you could provide just one sample or you may need to collect samples throughout a 24-hour period.
For the 24-hour urine test, you may be given instructions on when to start collecting urine. You record the time when you collect the first sample which is typically, the first urine of the day. Then you collect a sample every time you urinate over the next 24-hour period.
You’ll be given instructions on how to keep the samples either on ice or in the refrigerator. You’ll also be instructed on where to take the samples afterwards.
What Do My Results Mean?
You’ll be given your results in the form of milliequivalents per liter (mEq/L). The normal value may differ slightly depending on your lab.
For a one-time urine sample, the normal urine sodium value is around 20 mEq/L. For the 24-hour urine test, the norm ranges from 40 to 220 mEq/L per day. The wide range reflects your dietary salt intake.
Your doctor will compare results from the urine sodium test to the blood sodium test. Your results could show a high concentration of sodium in both the urine and blood tests. This can help your doctor determine if in the case of an acute kidney injury if the problem is ADH levels or tubular damage with a concentrating the urine secondary ATN . But you could also have high levels in the urine and have normal or low levels in your blood when your body is losing too much sodium.
Low sodium levels in the urine could indicate:
- Diarrhea and fluid loss
- Kidney problems
- Too much hormone released by adrenal glands, which is called hyperaldosteronism
- Release of too much anti-diuretic hormone (ADH) that causes retention of sodium and water; this happens in heart failure and in cirrhosis (scarring of the liver).
High sodium levels in the urine could indicate:
Are There Other Tests I Might Take?
You may have already had the sodium blood test. Your doctor may order additional tests to see how your kidneys are doing, which could include:
- Glomerular filtration rate, a test that measures creatinine levels in the blood and indicates health of the kidneys
- Electrolyte panel test, a blood test that measures levels of electrolytes such as sodium, potassium, and more
- Calcium, a blood test that checks calcium levels that could relate to conditions of the bone, heart, nerves, kidneys, and more
- Phosphorus, a blood or urine test that checks how much phosphorus is in your blood
- Blood urea nitrogen, or BUN, a blood test that measures how well your kidneys are getting rid of a waste product