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Magnesium test

Also called: Serum magnesium, Mg

A magnesium test measures magnesium in your blood. Low magnesium can cause cramps, twitching, and heart rhythm problems.

SampleA small tube of blood from a vein in your arm
Fasting?Usually not needed
ResultsUsually within 1 to 2 days
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

Blood levels don't always reflect total body magnesium.

Why it's done

  • Muscle cramps, twitching, or irregular heartbeat
  • Low potassium or calcium that's hard to correct
  • Long-term acid reducer (PPI) or water pill use, heavy drinking, or diarrhea

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
MagnesiumAbout 1.7 to 2.2 mg/dL

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

Causes include diarrhea, heavy drinking, PPIs, water pills, and poorly controlled diabetes.

High

Uncommon; usually from kidney disease plus magnesium-containing laxatives or antacids.

Questions to ask your provider

  • What do my results mean for me?
  • Do I need to repeat this test or have other tests?
  • Should I take a magnesium supplement?
  • Could my medicines be the cause?

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.