Why Do I Need a Blood Test for Sodium?

A sodium blood test is pretty straightforward: It measures the amount of sodium in your blood.

Sodium is key to helping send electrical signals between cells and controlling the amount of fluid in your body. Your body needs it for your cells to work the right way.

Most foods have sodium in them. The most common form is sodium chloride, found in table salt. Your body loses a certain amount of sodium each day through sweat and when you go to the bathroom.

A sodium blood test will measure your sodium level – because too little or too much can cause problems.


You might have certain symptoms that lead your doctor to suspect that your sodium level may be too high or too low. You might be confused, forgetful, or have problems with reasoning. Other symptoms your doctor may watch for include:

Things That Can Throw Your Sodium Off

Any number of things can cause your sodium levels to get out of whack. They include:

  • Surgery, an injury, or a serious illness
  • Eating or drinking too much salt or liquids -- or too little of them
  • Getting IV fluids
  • Taking a class of medications called diuretics, which lower the amount of fluid in your body
  • Taking other medicines, including the hormone aldosterone
  • Diabetes
  • Kidney problems

Your doctor might order a test if you’re showing signs of a sodium imbalance or are at risk of becoming imbalanced.

How Does the Test Work?

You might hear your doctor or nurse call this a serum sodium test. And it’s sometimes just one part of a broader set of tests.

For the test, a technician will draw blood, usually from the inside of the elbow area or back of the hand.

The technician will tie an elastic band around your arm so your veins will swell, which makes drawing blood easier. He will then insert a needle into the vein, and blood will collect in a glass vial or a tube. He’ll untie the band on your arm. After the blood is collected, he will take out the needle and cover the puncture site.

The risks of the test are very low. You might bleed at the puncture site and have a bruise there later. Right after the blood draw, you might feel lightheaded. Infection is possible any time the skin is broken.


What Do the Results Mean?

Abnormal levels on a sodium blood test can point to various conditions.

If your sodium levels are too high for the amount of water in your body, it’s called hypernatremia. If the levels are too low, that’s called hyponatremia.

Hypernatremia might indicate several things, including:


Hyponatremia might suggest conditions including:

  • Adrenal glands not producing enough hormones
  • Severe vomiting and/or diarrhea
  • Increase in fluid in your body from conditions such as cirrhosis, congestive heart failure, and kidney failure
  • A problem with the way your body releases an antidiuretic hormone
  • Too much of a hormone called vasopressin, which helps keep your body’s water level in balance
  • Use of certain medicines, including diuretics, certain antidepressants, and opioids
WebMD Medical Reference Reviewed by Louise Chang, MD on November 18, 2018



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Nemours (KidsHealth.org): “Basic Blood Tests.”

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University of California San Francisco Medical Center: “Medical Tests -- Serum Sodium.”

NIH. U.S. National Library of Medicine: “AVP gene.”

Johns Hopkins Medicine: “Adrenal Glands.”

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