Magnesium

Also written as: Mg, Serum magnesium

A mineral needed by nerves, muscles, and the heart; blood shows only a small slice of body stores.

What it measures

The concentration of magnesium in the blood. Only a tiny fraction of the body's magnesium circulates in blood - most sits inside bone and cells - so the blood level is an imperfect window on total stores.

Why a doctor orders it

Ordered when muscle cramps, weakness, heart rhythm changes, or low calcium or potassium results are being investigated. It is also commonly checked in people taking diuretics (water tablets) or certain long-term stomach acid medicines.

What is generally associated with a higher result

Broadly associated with reduced excretion by the kidneys and with magnesium-containing antacids, laxatives, or supplements. Raised levels are uncommon when kidney function is normal.

What is generally associated with a lower result

Broadly associated with low intake, alcohol use, gut conditions causing diarrhea or poor absorption, and a range of common medicines, including some diuretics and long-term acid-reducing tablets.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

Magnesium-containing supplements, antacids, or laxatives
Diuretics (water tablets) and some long-term acid-reducing medicines
Alcohol intake
Recent diarrhea or vomiting
Sample handling - a hemolyzed (damaged) sample can falsely raise the result

Questions to take to your appointment

Could any of my regular medicines be affecting my magnesium?
Should calcium and potassium be checked alongside it?
How well does a blood level reflect the body's overall magnesium stores?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

Support this site

This site is free, has no paywall, and takes no money from hospitals, insurers, or billing companies. If it helped, a coffee keeps it going.

Buy us a coffee