In brief
Measures magnesium in the blood, and sometimes the urine. Only about 1% of the body's magnesium is in the blood.
What it measures
Magnesium, an electrolyte found in every cell of the body.
Why it is done
To check magnesium levels in people with conditions that can cause low or high magnesium.
Reading the results
- Low magnesium is more common than high. Causes include low intake (seen in older people, people who are malnourished and with alcoholism), excessive alcohol, diarrhoea and long-term diuretic use.
- High magnesium is uncommon and mainly occurs with kidney failure, or with magnesium-containing antacids or laxatives when the kidneys are not working well.
Before the test
None.
What can affect the result
- Some medicines
- Antacids or laxatives containing magnesium
Related topics
Sources
Test information summarised from the sources listed on this page, read on 19 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.