Vitamins & minerals
Magnesium blood test
A magnesium blood test measures a mineral your body needs for hundreds of processes, including muscle and nerve function, energy production and a steady heartbeat. A blood level is a useful check, though it doesn't always reflect your total body stores, so it's interpreted alongside your symptoms.
- What it measures
- Magnesium, a mineral for muscles, nerves and energy
- Sample
- Venous blood sample
- Fasting
- Not required
- Also known as
- serum magnesium, Mg
- Included in 57 Health tests
- 2 panels, from £160
Magnesium reference range
Guide only| Category | Guide range |
|---|---|
| Adults | 0.7–1.0 mmol/L |
Most magnesium is inside cells and bone, so a blood level can be normal even when total body stores are somewhat low. It's affected by kidney function, gut losses (such as diarrhoea) and some medicines. Ranges vary by laboratory.
These are general UK adult guide ranges from public health sources, shown for orientation only. Reference ranges vary by laboratory, assay, age and sex, so your result is always interpreted against the range quoted by the analysing laboratory on your report.
What does a high magnesium level mean?
A high magnesium is uncommon and usually related to reduced kidney function or a very high intake (for example from some laxatives or antacids).
It's interpreted alongside kidney function and any supplements or medicines you take.
What does a low magnesium level mean?
A low magnesium can cause muscle cramps, twitching, fatigue and, if marked, heart-rhythm changes, and it can also lower calcium and potassium.
Common causes include poor intake, gut losses (diarrhoea or malabsorption), heavy alcohol use and some medicines such as certain diuretics and long-term acid reducers.
When to consider a magnesium test
- Muscle cramps, twitching or weakness
- Persistent fatigue
- Heavy alcohol use or a restricted diet
- Long-term use of diuretics or acid-reducing medicines
- Alongside calcium and potassium when these are abnormal
Frequently asked questions
This page is general information about a blood marker and is not medical advice or a diagnosis. A magnesium test screens and gives context; results are interpreted by a clinician alongside your symptoms, history and other markers. Always follow the guidance on your own report.