Serum Magnesium Test

Medically reviewed by Suzanne Falck, MD on December 21, 2017Written by Gretchen Holm on June 1, 2012

What is a serum magnesium test?

Magnesium is important to the functioning of your body and can be found in many common foods. Rich magnesium sources include green vegetables, nuts, seeds, and beans. Your tap water may also contain magnesium.

According to the National Institutes of Health (NIH), this mineral plays a role in more than 300 of your body’s biochemical reactions. For example, it helps regulate blood pressure and your heartbeat. It also helps maintain bone strength.

Having too little magnesium in your body can negatively affect all of these functions. It’s possible to have too much magnesium as well.

If your doctor suspects that your magnesium level is too low or too high, they may order a serum magnesium test. This test involves a basic blood draw. Your doctor will collect some of your blood into a vial or tube and send it to a lab for testing.

Why do I need a serum magnesium test?

The serum magnesium test isn’t included in the routine electrolyte panel, so there generally has to be a reason for your magnesium levels to be tested.

Your doctor may order a test if they suspect your magnesium level is too high or too low. Either extreme can lead to health problems. This test may also be ordered if you have chronic low potassium and calcium levels. Magnesium plays a role in regulating the calcium and potassium levels in your body. Your doctor may check your magnesium if these levels are consistently low.

This test may also be necessary if your doctor thinks you might have a malabsorption or malnutrition problem. You may have this test regularly if you take certain medications or have diabetes, kidney problems, or chronic diarrhea. Regular testing helps your doctor stay on top of your condition.

What are the symptoms of magnesium overdose?

The signs and symptoms of an overdose include:

On rare occasions, magnesium overdose can lead to cardiac arrest or death.

It’s rare to overdose on magnesium through food alone. The NIH provides a list of foods high in magnesium. Shredded wheat cereal, dry-roasted almonds, and boiled spinach are at the top of the list. Each one of these foods provides only about 20 percent of your daily value of magnesium per serving. Instead, magnesium overdose may be due to taking too many magnesium supplements.

People who take these supplements may be doing so to counter the symptoms of certain conditions, such as diabetes, alcohol use disorder, Crohn’s disease, or an issue absorbing nutrients. These supplements are also recommended for low potassium and calcium levels in the blood.

What are the symptoms of magnesium deficiency?

Symptoms of magnesium deficiency initially include:

As the deficiency progresses, you may experience:

What are the risks associated with the serum magnesium test?

You can expect to feel some minor pain during a blood draw. You might also continue to bleed slightly for a few minutes after the procedure. You may get a bruise at the needle insertion site.

Serious risks are rare and include fainting, infection, and inflammation.

What do the results mean?

The normal range for serum magnesium is 1.7 to 2.3 milligrams per deciliter for people 17 years old and up, according to Mayo Medical Laboratories.

The exact standards for normal results may vary depending on your:

  • age
  • health
  • body type
  • sex

The standards also depend on the lab performing the test. High and low magnesium levels have a wide variety of causes. Discuss your results with your doctor to get more precise information.

High magnesium levels

High levels of magnesium may result from taking too many supplements or from a problem with excreting extra magnesium.

Specific conditions that can lead to high magnesium levels include kidney failure and oliguria, or low urine production.

Low magnesium levels

Low levels, on the other hand, can indicate that you don’t eat enough foods containing this mineral. Sometimes low levels mean that your body isn’t keeping enough of the magnesium that you eat. This can happen in cases of:

  • chronic diarrhea
  • hemodialysis, a mechanical way to filter waste products from the blood when the kidneys don’t function properly
  • gastrointestinal disorders, such as Crohn’s disease
  • ongoing use of diuretics

There are quite a few other possible causes of low magnesium. These include:

Low levels can also occur due to alcohol use disorder and during the course of a condition called delirium tremens (DT). DT is caused by alcohol withdrawal and involves trembling, agitation, and hallucinations.

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