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Vitamins & Minerals

Magnesium

Magnesium is a mineral that helps your muscles, nerves and heart work and keeps your bones strong. Most of it is stored in your bones and muscles, so this blood test only catches the small amount travelling in your blood. A result inside the range on your report is the usual, reassuring picture. A low result is the more common finding and is something your GP can look into with you.

Standard Care
CategoryVitamins & Minerals
Reference range0.70–1.10 mmol/L mmol/L
Evidence✓Standard Care
Last updated3 July 2026
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What is magnesium?

Magnesium is a mineral involved in an enormous range of body processes. The RCPA lists the main ones: "making energy, muscle contraction, sending nerve signals and building strong bones and teeth" and "blood clotting and regulating blood pressure" and "production of insulin and helps cells to take up glucose which helps to control blood glucose levels." Healthdirect adds heart health to the list. Despite its importance, most magnesium is not in the blood at all. As healthdirect explains: "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." This matters because a blood magnesium test reflects only that small circulating fraction — a result within the reference range does not guarantee full body stores are adequate, and a result below the range confirms a deficit.

Why is it tested?

A magnesium test is usually ordered when there is a reason to suspect low levels — for instance, if you have symptoms such as muscle cramps, twitching, or fatigue, or if you have a condition that can impair magnesium absorption (such as coeliac disease or inflammatory bowel disease). It is also checked if you take medicines known to reduce magnesium, or if other electrolytes such as potassium or calcium are persistently low (since low magnesium can make these harder to correct). A raised magnesium is less commonly the reason for testing but may be found incidentally in people with kidney disease or taking magnesium-containing medicines.

Reference range (Australia)

0.70–1.10 mmol/L mmol/L

The AHRIA harmonised reference interval (AACB/RCPA-endorsed) applies to adults of all sexes. The range printed on your own report is the figure your GP uses for your result — use that range when reading it.

Reference intervals vary between laboratories. Always use the range printed on your own report.

What your result means

If your level is low

A magnesium below the reference range (hypomagnesaemia) is the more commonly encountered finding. The RCPA identifies several pathways: "not getting enough magnesium in your diet, or you are not able to absorb enough," "vomiting or diarrhoea," or conditions such as "coeliac disease or inflammatory bowel disease (Crohn's disease and ulcerative colitis)." Kidney disease and some medicines (including certain diuretics and long-term acid-suppression medicines) can also increase magnesium losses. Your GP will consider the likely cause before deciding whether any change is needed.

If your level is in range

A magnesium within the reference range is reassuring. Because the blood level reflects only a small fraction of total body magnesium, eating a varied diet that includes magnesium-rich foods — leafy greens, nuts, seeds, whole grains, and legumes — supports overall magnesium status beyond what the blood test alone can tell you.

If your level is high

A magnesium above the reference range (hypermagnesaemia) is uncommon in everyday testing. Healthdirect identifies the main causes: it may happen "with kidney failure, if you take medicines that contain magnesium, such as antacids or laxatives, if you take too many magnesium supplements." Because healthy kidneys clear excess magnesium efficiently, a raised level in someone with normal kidney function is unusual. Your GP will review your kidney results and any supplements or medicines you take.

What can affect your result

How much magnesium your body holds depends on three things working together: how much you take in from food, how well your gut absorbs it, and how much your kidneys let through into the urine. On the intake and absorption side: a diet low in magnesium-rich foods (leafy greens, nuts, seeds, whole grains, legumes), or a gut condition that impairs absorption (coeliac disease, Crohn's disease, or ulcerative colitis), can gradually lower magnesium. Persistent vomiting or diarrhoea causes direct losses from the gut. On the excretion side: the kidneys normally conserve magnesium tightly, but kidney disease can impair this. Some medicines increase urinary magnesium loss — certain diuretics and some other medicines used for infections or cancer are known examples. Long-term use of acid-suppression medicines (proton pump inhibitors — commonly used for reflux) can also reduce magnesium absorption over time. On the high side: magnesium-containing antacids or laxatives, or high-dose supplements, can raise the blood level, particularly in someone whose kidneys are not clearing it efficiently.

When to act

If your magnesium is outside the reference range, your GP will look at the likely cause in context — your diet, any gut conditions, your medicines, and your kidney function. Low magnesium alongside low potassium or calcium is worth looking into because a magnesium deficit can make those other electrolytes harder to correct. Symptoms such as muscle cramps, twitching, or a fluttering heartbeat alongside a low magnesium result are worth mentioning when you speak to your GP — they help prioritise next steps. This page is general information and is not a substitute for advice from your GP.

Frequently asked questions

The harmonised reference interval endorsed by the AACB and the RCPA is 0.70–1.10 mmol/L for adults. The range printed on your own laboratory report is the one your GP will use — laboratories can set their own intervals, so your report is the right reference.

Your body uses bone as a storage reservoir for several minerals, including calcium and magnesium. As healthdirect explains, "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." This means the blood level can look normal even when total body stores are becoming depleted — and it can fall below the range when the body can no longer draw enough from reserves.

The most common causes are not getting enough magnesium from the diet, or not absorbing it efficiently — the RCPA notes this can happen with gut conditions such as coeliac disease or inflammatory bowel disease (Crohn's disease and ulcerative colitis). Persistent vomiting or diarrhoea causes direct losses. Some medicines — including certain diuretics and long-term acid-suppression medicines — increase how much magnesium is lost through the urine. Your GP will weigh up which is most likely based on your history.

High magnesium is uncommon in people with normal kidney function, because healthy kidneys clear excess magnesium efficiently. When it does occur, healthdirect identifies the common reasons: kidney failure (which reduces clearance), taking medicines that contain magnesium such as antacids or laxatives, or taking too many magnesium supplements. Your GP will check your kidney function alongside the magnesium result.

Yes. The gut is where magnesium from food is absorbed, so conditions that impair absorption — such as coeliac disease and inflammatory bowel disease (Crohn's disease and ulcerative colitis) — are recognised causes of magnesium deficiency. If your magnesium is persistently low and you have a known gut condition, your GP will consider whether that connection is relevant to your results.

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