What is a magnesium blood test?

A magnesium blood test measures how much magnesium is in your blood.

Magnesium is an important mineral for many body functions, including:

• muscle and nerve function
• heart health
• bone strength

Your body gets most of its magnesium from food. Learn more about foods high in magnesium.

Most magnesium is stored in your bones. Some of it can be released when needed. The rest is found in your muscles and soft tissues. Only a very small amount of magnesium circulates in your blood.

When is a magnesium blood test used?

Your doctor might order a magnesium blood test if you:

• are older
• drink a lot of alcohol
• have a diet that may not provide enough magnesium
• have symptoms of low or high magnesium levels — such as muscle cramps, irregular heartbeat, tiredness, headaches or seizures
• have a health condition — such as a heart condition, kidney disease, diabetes or hyperparathyroidism
• have digestive problems — such as Crohn's disease or ongoing diarrhoea
• take certain medicines or receive treatment — such as diuretics (fluid tablets) or some cancer treatments

Where can I get a magnesium blood test?

You usually need to go to a pathology collection centre with a referral from your doctor. Your doctor will recommend one near you.

Sometimes, your doctor will collect blood for testing in their clinic. Blood tests are also routinely done in hospitals.

How do I prepare for a magnesium blood test?

No special preparation is usually required for a magnesium blood test.

Certain medicines and supplements can affect your magnesium levels. Let your doctor know about any medicines and supplements you are taking.

If you are having other blood tests done at the same time, there may be more instructions to follow. Check with your doctor or the pathology collection centre if there is anything you need to do before your blood test.

What happens during a magnesium blood test?

A health professional will take a sample of blood, usually from a vein in your arm. The blood will then be sent to a laboratory for testing.

What do my magnesium blood test results mean?

A result outside the normal range doesn't always mean you have a health problem. Your doctor will help you understand what your results mean.

Low levels of magnesium may be caused by:

• not getting enough magnesium from your diet
• losing magnesium through vomiting or diarrhoea
• not absorbing enough magnesium in your intestines

High levels of magnesium may happen:

• with kidney failure
• if you take medicines that contain magnesium, such as antacids or laxatives
• if you take too many magnesium supplements

Talk to your doctor about your blood test results and what they mean for you. Always check with your doctor before taking magnesium supplements.

Resources and support

Pathology Tests Explained has information about magnesium blood tests.

Read our 'Guide to blood testing' to learn more about blood tests, including:

• what to consider before having the test
• what happens during a blood test
• how accurate results are
• blood test costs

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available 24 hours a day, 7 days a week.