Serum Magnesium Test

Written by Gretchen Holm | Published on June 1, 2012
Medically Reviewed by George Krucik, MD

What Is a Serum Magnesium Test?

Magnesium is important to the functioning of your body. According to the National Institutes of Health’s Office of Dietary Supplements, this mineral plays a role in more than 300 of your body’s biochemical reactions (NIH: ODS, 2009). 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.

Many common foods contain magnesium. Rich sources include spinach and other green vegetables, nuts, seeds, and beans. Your tap water may also contain magnesium.

On the other hand, it’s possible to have too much. In rare cases, magnesium overdoses can lead to cardiac arrest and death. It’s rare to overdose on food alone. Instead, magnesium overdose may be caused by ingesting too many magnesium supplements.

Your doctor might have you take supplements if you have certain conditions such as diabetes, alcoholism, or malabsorptive issues. You may also take them if you have low potassium and calcium levels in your blood.

If your doctor suspects that your magnesium level is too low or too high, he or she may order a serum magnesium test.

All this test involves on your part is a basic blood draw. Your doctor will collect some of your blood into a vial or tube. This blood is then tested at a lab.

Why Doctors Perform a Serum Magnesium Test

Your doctor may order a serum magnesium test if he or she suspects that your magnesium level is too low or too high. Either extreme can lead to health problems. He or she may also order this test if you have chronically low potassium and calcium levels. Magnesium plays a role in regulating the calcium and potassium levels in your body. If these levels are consistently low, your doctor may check your magnesium.

This test may also be ordered if your doctor thinks you might have a malabsorption or malnutrition problem. If you have diabetes or kidney problems, you may undergo this test regularly. This helps your doctor stay on top of your condition.

Symptoms of magnesia deficiency initially include:

  • appetite loss
  • fatigue
  • nausea
  • vomiting
  • weakness

As the deficiency progresses, you may experience:

  • numbness and tingling
  • seizures
  • muscle cramps
  • personality changes
  • abnormal heart rhythms

Symptoms of an overdose include:

  • cardiac arrest (rare)
  • confusion
  • death (rare)
  • diarrhea
  • nausea
  • slowed heart rate
  • upset stomach
  • vomiting
  • very low blood pressure

If you have enough of these symptoms, your doctor might order this test.

The National Institutes of Health’s Office of Dietary Supplements provides a list of foods high in magnesium. Wheat bran, dry roasted almonds, and cooked frozen spinach are at the top of the list. Each one of these foods provides only about 20 percent of your daily value of magnesium in a serving (NIH: ODS, 2009).

As you can see, it would be hard to eat too much magnesium. Overdoses usually happen when someone consumes too much supplemental magnesium. You may be told to take supplements if you have diabetes or alcoholism. Your doctor may also instruct you to take them if you suffer from Crohn’s disease.

Normal Serum Magnesium Test Results

Serum magnesium is measured in milligrams per deciliter (mg/dL). A normal range is 1.7 to 2.3 milligrams per deciliter.

The exact standards for normal results may vary depending on your age, health, body type, and sex, as well as the lab performing the test. Discuss your results with your doctor to get more precise information.

What Do Abnormal Serum Magnesium Test Results Mean?

High levels of magnesium usually do not come from consuming too much as part of your diet. Instead, they can result from ingesting too much in supplement form. In other cases, high levels are caused by a problem with excreting the extra.

Specific conditions that can lead to high test results include:

Low levels, on the other hand, can indicate that you don’t eat enough of 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 do not function properly
  • Crohn’s disease, an inflammation of the bowel, or other gastrointestinal disorders
  • ongoing use of diuretics

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

  • heavy periods
  • issues with specific conditions, including hepatic cirrhosis, hyperaldosteronism, and hypoparathyroidism
  • severe burns
  • pancreatitis
  • sweating (in excess)
  • toxemia of pregnancy
  • ulcerative colitis, an inflammation of the bowel that affects the large intestine
  • uncontrolled diabetes

Low levels can also occur in alcoholism and during delirium tremens, trembling, agitation, and hallucinations caused by alcohol withdrawal.

Due to the wide range of causes of high and low magnesium levels, there’s no reason to jump to conclusions. Instead, work with your doctor to find out what’s causing your symptoms.

Risks of the Serum Magnesium Test

Any time you have your blood drawn, you can expect to feel some minor pain during the procedure. 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 complications are rare. You might faint during the procedure. You may get an infection or have vein inflammation.

Problems with the Serum Magnesium Test

A serum magnesium test may not accurately measure your magnesium levels. Dr. Carolyn Dean, MD, ND, author of The Magnesium Miracle, points out that less than one percent of your body’s magnesium is in your blood. She claims that this means the magnesium levels in your blood are not necessarily representative of your overall magnesium levels (Nutritional Magnesium Association, 2010).

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