What Is a Magnesium Test?

Medically Reviewed by Carol DerSarkissian, MD on May 10, 2021

Magnesium is a mineral found in the earth’s crust, and in your body. It’s needed for healthy bones, heart, muscles, and nerves. It helps your body control energy, blood sugar, blood pressure, and many other processes.

You get magnesium naturally in many foods. Some of these are peanut butter, nuts, spinach, beans, whole grains, bananas, milk, and salmon. It’s added to some breakfast cereals, bottled water, and other foods that you can buy.

Is Your Level Too Low?

Some people don’t get enough magnesium. If you’re basically healthy, you probably wouldn’t have symptoms from low magnesium unless it went on for a long time.

Your doctor may want to test your magnesium level. This is important because too much or too little can make both adults and children sick.

You might have trouble absorbing magnesium from food if you drink too much alcohol, have kidney problems, take certain medicines, or have celiac disease or long-lasting digestive problems.

If you are low on magnesium for a long time and it becomes magnesium deficiency, which is rare, you may have:

Extreme cases can cause muscle spasms and tremors (shakes that you can’t control).

Over time, low magnesium can weaken your bones, give you bad headaches, make you feel nervous, and even hurt your heart. It can also lead to low levels of other important minerals like calcium and potassium.

High levels of magnesium are much less common than low levels. This happens to people who have damaged kidneys, or take certain drugs. It is a serious problem that can cause your heart to stop.

Blood Test for Magnesium

Your doctor may order a magnesium test if you have signs of a problem, or if you have diabetes or kidney trouble. A blood test is the most common way to find out your magnesium level. You may hear the term “total serum magnesium test.”

The magnesium blood test is like other blood tests you may have had. A nurse or other health worker will clean your skin, insert a needle into a vein in your arm or hand, and take a sample of blood. It should feel like a pinprick, but not much more. Afterward, the nurse will take the needle out and may cover the area with a bandage in case it bleeds a little.

Within a few days, the doctor will look at the test results and should talk to you about what they mean. Low levels might mean you don’t get enough magnesium in your diet and need to take extra. Or, your body might get rid of more magnesium than it should.

People who have had recent surgery sometimes have low magnesium levels. It can also be a sign of diabetes, thyroid trouble, a problem with your pregnancy, or other health issues.

Other Magnesium Tests

Some experts don’t think a blood test is the best way to find out your magnesium level. That’s because much of the magnesium in your body is stored in your bones and other places, not in the blood.

Stress can send magnesium out of your cells and into your blood. This can make it seem like you have more magnesium in your body than you really have if you simply have a blood test.

There are other tests. Some of them:

  • Test how much magnesium you get rid of in your pee.
  • Test the level of magnesium in your red blood cells (RBC).
  • Test the magnesium in your cells, not in your blood. This test is known as an “EXA Test,” and is done through a sample of your mouth cells. It is not easy to get this test because it is not commonly known and it is very expensive.
  • Add magnesium to your blood, then see how much goes into your urine.

Talk with your doctor so you understand your results and whether you need more tests.

Show Sources


Clinical Kidney Journal: “Magnesium Basics.”

National Institutes of Health, Office of Dietary Supplements:  “Magnesium Fact Sheet for Consumer,” “Magnesium Fact Sheet for Health Professionals.”

Harvard Health Publications: “What You Should Know About Magnesium.”

The Merck Manual, Home Edition, Chapter 137, “Salt Balance.”

Nutritional Magnesium Association, “Blood Serum Invalid Measure of

Magnesium Deficiency.”

Lab Tests Online: “Magnesium.”

TeensHealth from Nemours: “Blood Test: Magnesium.”

Magnesium Deficiency Resource: “Magnesium Deficiency Testing.”

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