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Sodium

(Na)

What Is Sodium?

Sodium is an electrolyte. The body needs it to work as it should. It can be found in all fluids in the body. Sodium regulates blood pressure and fluid levels in the body. Sodium gets into the blood through food and drink. It leaves in urine, stool, and sweat.

Reason for the Test

The test measures the sodium level in the blood. A sodium test can be used:

  • As part of a routine check up with other blood tests
  • When symptoms point to sodium levels that are too high or too low
  • To see how well treatment is working for certain health problems such as high blood pressure, heart failure, or kidney disease

A urine test is done when a blood test shows an abnormal result. It can help find the cause of a problem or see how well treatment is working.

Type of Sample Taken

A sample may be:

  • Blood taken from a vein in the arm
  • A urine test

Prior to Collecting the Sample

Tell your doctor about any medicines or supplements you are taking. They may affect the test results.

During the Sample Collection

You will be asked to sit. An area inside your elbow will be cleaned. A large band will be tied around your arm. The needle will then be inserted into a vein. A tube will collect the blood from the needle. The band on your arm will be removed. Once all the blood is collected, the needle will be removed. Some gauze will be placed over the site to help stop bleeding. You may also be given a bandage to place over the site. The process takes about 5 to 10 minutes.

For a urine test, you will pass urine into a special container.

After Collecting the Sample

After the blood sample is taken, you may need to stay seated for 10 to 15 minutes. If you are lightheaded, you may need to stay seated longer. When you feel better, you can leave.

A bit of blood may ooze from the vein beneath the skin. It will cause a bruise. Firm pressure over the site after the needle is removed will decrease the chance of a bruise. A bruise will usually fade in a day or 2.

Call your doctor right away if you have redness, swelling, lasting bleeding, or pain.

There will be no problems after a urine test.

Results

Results should take a few hours to a few days.

A lower than normal sodium level in the blood is called hyponatremia. It can happen when:

  • Too much sodium is lost—such as with diarrhea, certain medicines, or kidney disease
  • There is too much fluid in the body—can happen with heart failure, or liver or kidney disease

A higher than normal sodium level in the blood is called hypernatremia. It can happen:

  • When too much water is lost without drinking enough to make up for it—dehydration
  • With major skin burns, kidney disease, diabetes insipidus, or adrenal gland problems

Sodium levels may also not be normal because of:

  • High blood glucose
  • Very high levels of cholesterol or other fats in the blood
  • Very high or low levels of protein in the blood

Sodium levels from a urine test are compared to those in the blood. The results can mean:

  • Both blood and urine sodium levels are higher than normal—May mean sodium levels are very high.
  • Blood levels are lower than normal, but urine levels are higher than normal—May mean too much sodium is passing in the urine.
  • Both blood and urine sodium levels are lower than normal—May mean sodium levels are too low.

Your doctor will talk to you about the results. A test may point to an illness that you do not have. It can also miss an illness that you may have. The doctor will check your symptoms and all test results before making a diagnosis.

REFERENCES:

Sodium. Lab Tests Online—American Association of Clinical Chemistry website. Available at: https://labtestsonline.org/tests/sodium. Updated May 13, 2019. Accessed July 26, 2019.

Sodium measurement, serum. EBSCO DynaMed website. Available at:https://www.dynamed.com/lab-monograph/sodium-measurement-serum. Updated October 8, 2018. Accessed July 26, 2019.

Last reviewed June 2019 by EBSCO Medical Review Board Nicole S. Meregian, PA