Magnesium

Involved in several hundred enzyme reactions. Less than one per cent of the body’s magnesium sits in blood, so a low result is meaningful but a normal one does not rule depletion out.

Magnesium in the Biomarker Guide — what it is, why it is tested, and what moves the number.

Add-on markers can only be added to venous samples.

Timing

Take in the morning, before any supplements. Serum magnesium dips after food and drifts through the day. If you take magnesium, leave at least 24 hours between the last dose and the sample, or you are measuring the dose rather than your stores.

Turnaround: the lab reports this test within 24 hours of receiving your sample, counted in working days. Most samples reach them within about 3 days of posting. Full detail on our Turnaround Times page.

We do not interpret results. Not medical advice or a diagnosis.