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Sodium test

Also called: Serum sodium, Na

A sodium test measures sodium in your blood. Low sodium can cause confusion, headache, and seizures.

SampleA small tube of blood from a vein in your arm
Fasting?Usually not needed
ResultsOften the same day
Good to knowOne result rarely tells the whole story. Your provider looks at your results together with your symptoms, exam, and other tests.

What the test is

Sodium levels mostly reflect the balance of water in your body.

Why it's done

  • Confusion, weakness, nausea, or seizures
  • Monitoring water pills and some antidepressants and seizure medicines
  • Heart, kidney, or liver disease

Getting ready and what happens

  • No special preparation is needed.

How the test is done

  • A health worker cleans the skin, puts a band around your arm, and draws blood from a vein with a small needle. It takes a few minutes.

What the results mean

ResultTypical range for adults
Sodium135 to 145 mEq/L

Normal ranges vary from lab to lab and can differ by age, sex, and pregnancy. Your report lists your lab's own range next to each result. A result a little outside the range is often not a problem.

Low (hyponatremia)

Causes include water pills, some antidepressants, drinking very large amounts of water, heart failure, and liver or kidney disease.

High (hypernatremia)

Usually from not drinking enough water, often in older adults or with illness.

When a result needs quick action

Call 911Low or high sodium with confusion, a seizure, or extreme sleepiness

Questions to ask your provider

  • What do my results mean for me?
  • Do I need to repeat this test or have other tests?
  • What's causing my abnormal sodium?
  • Should I change how much I drink?

Risks

A blood draw is very safe. You may have slight pain or a small bruise where the needle went in.

Related conditions

Related medicines

Related tests

Sources

Last updated 2026-11-13.