What is a sodium blood test?

A sodium blood test measures the amount of sodium in your blood. Sodium is a type of electrolyte. Electrolytes are minerals that have an electrical charge when they are dissolved in water or body fluids. You have electrolytes in your blood, urine (pee), tissues, and other body fluids. They help control the amount of fluid and the balance of acids and bases (pH balance) in your body. Sodium also helps your nerves and muscles work properly.

You get most of the sodium you need in your diet. If you take in too much, your kidneys get rid of the extra sodium in your urine (pee). Normally, your body keeps your sodium levels in a very narrow range. If your sodium blood levels are too high or too low, it may mean that you have a kidney problem, dehydration, or another type of medical condition.

Other names: Na test

What is it used for?

A sodium blood test is a routine test that may be used to check your general health. It may be used to help find and monitor conditions that affect the balance of fluids, electrolytes, and acidity in your body.

The test is often done as part of a group of tests called an electrolyte panel. It may also be part of two other groups of tests called a basic metabolic panel (BMP) and a comprehensive metabolic panel (CMP).

Why do I need a sodium blood test?

Your health care provider may order a sodium blood test as part of your routine checkup or if you take medicines that can affect your fluid balance. You may also have this test if you have symptoms of too much or too little sodium in your blood.

Symptoms of high sodium levels (hypernatremia) include:

• Thirst
• Urinating (peeing) very little
• Vomiting
• Diarrhea
• Confusion
• Muscle twitching
• Seizures

Without treatment, extremely high levels of sodium may lead to a coma and become life-threatening.

Symptoms of low sodium levels (hyponatremia) include:

• Weakness
• Fatigue
• Confusion
• Muscle twitching
• Seizures

Without treatment, extremely low levels of sodium may also lead to a coma and become life-threatening.

What happens during a sodium blood test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

Your provider will let you know how to prepare for a sodium blood test. You may need to stop taking certain medicines before this test, so tell your provider about everything you take. But don't stop any medicines unless your provider tells you to.

You may also need to fast (not eat or drink) for several hours before the test. Ask your provider if you have any questions.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Blood sodium levels that are too high or too low can be a sign of many different conditions. To make a diagnosis, your provider will usually look at the results of your sodium blood test with the results of other tests, such as measurements of other electrolytes.

Sodium blood test results that are higher than normal may be a sign of a condition such as:

• Dehydration, which may be caused by not drinking enough, diarrhea, or taking diuretic medicines (water pills)
• A disorder of the adrenal glands
• A kidney disease
• Diabetes insipidus (uncommon)

Sodium blood test results that are lower than normal may be a sign of a condition, such as:

• A loss of sodium from diarrhea or vomiting
• A condition that may cause the body to hold onto extra fluid (which dilutes sodium), including:
  • Kidney diseases
  • Cirrhosis of the liver
  • Heart failure
  • Certain brain and lung diseases
  • Certain types of cancer
  • Certain medicines, including many over-the-counter pain relievers and some antidepressants
• Addison disease
• Malnutrition

If your results are not in the normal range, it doesn't always mean that you have a medical condition that needs treatment. Certain medicines, your age, sex, and certain medical conditions can increase or decrease your sodium levels. If you have questions about your results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I should know about a sodium blood test?

Sodium levels are often measured with other electrolytes in another test called the anion gap. An anion gap test looks at the difference between negatively charged and positively charged electrolytes. The test checks for acid imbalances and other conditions.