What Is a Magnesium Test?

Magnesium is a plentiful mineral in the body, and it plays a central role in many chemical reactions—more than 300 different ones. According to the National Institutes of Health (NIH), some of the ways magnesium assists the body include:

  • Protein synthesis
  • The function of muscles and nerves
  • Managing blood glucose levels
  • Maintaining blood pressure
  • Facilitating energy production
  • The formation of bone
  • Synthesizing antioxidants in the body
  • Nerve conduction and contraction of the heart

Magnesium is naturally-occurring in many of the foods you eat, and some foods may be enriched with it. It can also be found in some over-the-counter medications and it can be purchased as a supplement as well.

Nurse observing the blood
Yoshiyoshi Hirokawa / Getty Images

Purpose of the Test

The purpose of a magnesium test is to determine whether your levels are too low or too high. In the early stages of magnesium deficiency, a person may experience fatigue, reduced appetite, weakness, nausea, and vomiting. They may describe numbness and tingling in their extremities, leg cramps, or a change in heart rate.

Low levels of magnesium may correlate with an increased risk of chronic and inflammatory diseases and can contribute to conditions like high blood pressure, headaches, diseases of the cardiovascular system, arrhythmias, and osteoporosis.

In contrast, high levels of magnesium may lead to symptoms like an irregular heartbeat, low blood pressure, slow respirations, bouts of confusion, and more.

Your healthcare provider may choose to have you undergo a magnesium test, which is a blood test, usually if he/she suspects you may be exhibiting signs of abnormal magnesium levels. The test will help your practitioner gain a better understanding of the amount of magnesium in your blood. Additionally, if you have atypical calcium or potassium levels, your healthcare provider may want to evaluate your magnesium levels, too.

Risk and Contraindications

The risks and contraindications for a magnesium test are similar to those of any blood test. In general, blood tests have a very low risk of complications. However, sometimes a person may have veins that make it difficult to collect blood or that move during the process.

For those individuals, the healthcare provider may need to insert the needle more than once to obtain a blood sample. When having blood drawn for this test, you may experience:

  • A minor poke or stinging sensation at the site
  • Bruising at the location of the insertion site
  • A feeling of faintness or lightheadedness
  • An accumulation of blood under the skin (also known as a hematoma)
  • Excessive bleeding
  • Pain related to having more than one puncture to find a vein
  • A swollen or inflamed vein (also known as phlebitis)
  • An infection

Bruising may be alleviated or minimized by keeping a bandage in place for the amount of time the clinician recommends following the blood draw. In the unlikely event that phlebitis occurs, it’s often treated using warm compresses throughout the day.

Before the Test

Typically, there are no specific preparations required to have this blood test. To facilitate easy access to your veins, make sure you wear a shirt that allows you to roll it up above the elbows. Also, some medications like antacids, laxatives, and Epsom salts contain magnesium and may interfere with the blood test.

Let your healthcare provider know about all the drugs you’re taking, including over-the-counter medications and supplements. Your healthcare provider might ask you to stop taking them for a few days before the test for the most accurate results.

On the day of the test, be sure to have your insurance card and a form of identification with you so that blood work can be billed to your insurance carrier without delay. You may want to talk with your insurance company about whether or not the blood test requires pre-approval.

During the Test

A magnesium test is done in much the same way as other blood tests. You’ll likely be seated in a chair so that you can rest the arm where the blood will be taken from. The technician, nurse, or another healthcare provider will place an elastic band around your arm to temporarily restrict the flow of blood and locate a vein. Once a vein is found, the healthcare provider will disinfect the area, usually with an alcohol swab or pad, before inserting the needle.

After the needle has been inserted into the vein, the technician will place a vial at the end of the syringe to collect the sample. When a sufficient amount of blood has been obtained, the technician will remove the elastic and place an adhesive or bandage over the insertion site. The whole procedure should take no more than a couple of minutes.

After the Test

You may notice a bit of pain at the injection site, but this should go away within a few days. Your technician may also want you to keep the bandage on for a few hours to decrease the likelihood of experiencing any bruising.

Generally, there are few follow-up instructions (if any) after a magnesium test, and you’re able to resume your normal activities. Your healthcare provider should notify you once the results are back and provide you with any specific follow-up instructions you might need.

Interpreting the Results

Each lab may have a particular guide or reference range for what is considered normal. As an example from the NIH, a normal range is from 1.7 to 2.2 mg/dL. A high magnesium test may indicate health conditions such as:

  • Problems with the adrenal glands
  • Kidney impairment
  • Dehydration
  • Diabetic ketoacidosis, which can have life-threatening consequences in people with diabetes
  • Decreased urinary output
  • Disease of the parathyroid glands
  • Tumor lysis syndrome (a complication experienced by some people with cancer)

High levels of magnesium may also occur in people who take lithium as well as in those who take laxatives, Epsom salts, certain supplements, or use enemas.

On the other hand, low magnesium levels can be indicative of conditions like:

  • Alcoholism
  • Chronic cases of diarrhea
  • Reduced liver function
  • Trouble with the parathyroid gland
  • Pancreatitis
  • Inflammation of the intestinal tract, which can be seen in illnesses like ulcerative colitis
  • Preeclampsia—if pregnant
  • Uncontrolled diabetes

Medications that can cause low magnesium include diuretics, some antibiotics, some chemotherapy agents, and heart medications such as digoxin.

Bear in mind that your physician will help you interpret your test results and assist in determining the appropriate course of treatment if need be.

A Word From Verywell

Blood tests are a commonly performed procedure, but an open line of communication between a patient and a physician is always beneficial whenever you’re having a test done. If you have any questions or concerns about a magnesium test, be sure to speak with your healthcare provider about them so that you’re aware of why you’re undergoing the test, the risks involved, and what the test results can mean for you.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Institutes of Health. Magnesium.

  2. MedlinePlus. Superficial thrombophlebitis.

  3. MedlinePlus. Magnesium blood test.

Additional Reading

By Jenny Lelwica Buttaccio, OTR/L
Jenny Lelwica Buttaccio, OTR/L, is a licensed occupational therapist and advocate for patients with Lyme disease.