Summary

• Magnesium is an important electrolyte that your body needs for making energy, muscle contraction, sending nerve signals and building strong bones and teeth.
• Magnesium also has a role in blood clotting and regulating blood pressure. It is also involved in the production of insulin and helps cells to take up glucose which helps to control blood glucose levels.
• You get magnesium from your diet, and it is absorbed in the small intestine.
• Because magnesium is used in so many of the body’s functions, measuring magnesium levels is used to diagnose and manage a wide range of health conditions.
• The test usually measures the magnesium level in your blood, but sometimes urine is tested.

What is magnesium?

Magnesium is an electrolyte that is found in every cell of your body. Electrolytes are minerals that have an electric charge when dissolved in water – or blood. In your body, they help regulate many systems including heart rhythms, nerves and muscles. They are also involved in helping maintain the amount of fluid and the acid-base balance in your body.

About half of the body’s magnesium is combined with calcium and phosphate to form your bones. About 40 percent is found in muscles and soft tissues. Only a very small amount (about one percent of the total magnesium in the body) is found in the blood.

The levels of magnesium in your blood, tissues, and bone depend on how much is absorbed from your intestines and how much is removed or retained by your kidneys.

How you get magnesium from your diet

Intestines absorb magnesium from your diet. If you are not getting enough magnesium, it may be because there is not enough in your diet, or you are not able to absorb enough, such as if have vomiting or diarrhoea. Conditions in your gut which impact your intestines’ ability to absorb magnesium such as coeliac disease or inflammatory bowel disease (Crohn’s disease and ulcerative colitis) may also affect levels.

How excess magnesium is removed from your body

Kidneys filter excess magnesium from your blood, and it is removed in your urine. If your magnesium level is low, your kidneys respond by reducing the amount being removed through urine. Abnormal magnesium levels are seen in conditions or diseases that cause too little or too much magnesium to be removed by the kidneys.

Magnesium is needed by your body to properly absorb calcium from your diet and for the body to use calcium effectively.

Calcium levels are regulated through a feedback system that is controlled by the parathyroid glands. These are located behind your thyroid at the base of your neck.

The parathyroid glands release parathyroid hormone (PTH) to signal to your intestines, bones and kidneys, which all play a part in keeping calcium, phosphate levels and vitamin D in balance. For more on this see Calcium, phosphate and magnesium and Calcium.

Magnesium helps convert vitamin D into its active form, calcitriol, which is needed for calcium absorption. It is also needed for making and releasing PTH. When magnesium levels are low, not enough PTH is produced, leading to lower calcium levels. A low magnesium level can, over time, cause persistently low calcium levels. This means that measuring magnesium can be helpful in diagnosing disorders that involve calcium, potassium, phosphate and/or PTH.

Why get tested?

• Too little magnesium and you are said to have magnesium deficiency or hypomagnesaemia.
• Too much magnesium, and you have hypermagnesemia.

You may need to have your magnesium levels checked to monitor your health if you have a condition that causes you to:

Lose too much magnesium through your kidneys

• chronic kidney disease
• uncontrolled diabetes
• excessive alcohol intake

Lose magnesium through your gastrointestinal tract (your gut)

• acute or chronic diarrhoea

Fail to absorb enough magnesium through your intestines

• inflammatory bowel disease (IBD).
• coeliac disease

There are also medications that can increase magnesium levels. These include:

• diuretics
• certain antibiotics
• proton pump inhibitors to reduce stomach acid
• chemotherapy drugs
• anti-rejection drugs (for after you have had an organ transplant)
• aspirin
• products that contain magnesium, including laxatives and antacids
• lithium

Urine magnesium

Sometimes magnesium testing is done on a urine sample. This is to see if a low blood magnesium level is due to loss through the kidneys or due to gastrointestinal malabsorption.

Having the test

Sample

Blood and/or urine.

Any preparation?

None.

Your results

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Reference intervals

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people
• When compared against them your results may be flagged high or low if they sit outside this range
• Many reference intervals vary between labs so only those that are standardised or common across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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