BiomarkersMagnesium (serum)

Minerals

Magnesium (serum)

Mineral for muscles, nerves, sleep and blood sugar

On your report it may say: Serum Mg

Magnesium is involved in hundreds of body processes, from muscle relaxation to blood sugar control. Only about 1% of your magnesium is in the blood, so a normal serum result doesn't rule out low body stores.

Updated 2026-10-26

Typical ranges · mg/dL

Low below 1.7
Low end of range 1.7–2
In range 2–2.4
High 2.4+

mmol/L = mg/dL × 0.411

Kidney function strongly affects magnesium, so it's read with kidney tests.

Ranges vary by lab, age and sex. The range printed on your report applies.

If it's low

Blood magnesium is low, which usually means body stores are also low.

Common causes

  • Low intake of greens, nuts and whole grains
  • Acid-reducing medicines (PPIs) and diuretics
  • Diarrhoea
  • Alcohol
  • Poorly controlled diabetes

What you might notice

  • Muscle cramps or twitches
  • Poor sleep
  • Tiredness
  • Irregular heartbeat in severe cases

If it's high

High magnesium is uncommon and usually linked to kidney problems or very high supplement or laxative use.

Common causes

  • Kidney disease
  • Magnesium-containing laxatives or antacids
  • Very high supplement doses

What you might notice

  • Nausea
  • Weakness
  • Low blood pressure

Testing

Who should test
People with cramps, on PPIs or diuretics, with diabetes, or with heart rhythm concerns.
How to prepare
No fasting needed; avoid supplements on the morning of the test.
When to retest
8–12 weeks after a change.

What can help

Food sources

Pumpkin and sesame seedsAlmonds and cashewsSpinachBajra, ragi and whole grainsDark chocolate

See a doctor if magnesium is high, or low with palpitations, or if you have kidney disease.

Common questions

Why can serum magnesium look normal when I'm low?

The body keeps blood levels steady by pulling from bones and cells.

Is RBC magnesium better?

It reflects cell levels more closely, but ranges vary between labs.

Explore further

Sources

  1. MedlinePlus (US National Library of Medicine): Magnesium blood test
  2. NIH Office of Dietary Supplements: Magnesium fact sheet for health professionals

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For general education only, not medical advice. Ranges shown are typical for adults; the range printed on your lab report applies. Talk to a qualified doctor about your results.