Magnesium
A mineral for muscles, nerves, sleep and heart rhythm. Most of it lives inside cells, so a normal blood level doesn’t always mean you have enough.
TypeBlood test
HowStandard blood draw.
How oftenIf symptoms or on certain medicines.
BeforeNo preparation.
WhoPeople with cramps, palpitations, on diuretics or acid-reducing medicines.
Why a normal blood level can mislead
Almost all your magnesium sits inside bones and cells, not in blood. The body keeps blood levels steady, so a normal result doesn’t fully rule out low stores.
Blood (serum)
“Is it dangerously low?”
The standard test. Catches large drops.
Standard
Red cell magnesium
“What about inside cells?”
Sometimes used, but evidence is mixed.
Limited
Symptoms and risk
“Should I consider it anyway?”
Cramps, diuretics, acid-reducers, diabetes or alcohol raise the chance of low stores.
Context matters
Is it right for you?
Worth considering if…
- You have muscle cramps or palpitations.
- You take diuretics or acid-reducing medicines long term.
- You have diabetes or heavy alcohol use.
A better option if…
- You feel well with no risk factors - routine testing is rarely useful.
How it’s measured
Serum magnesium
The standard test; can look normal even when stores are low.
RBC magnesium
Measures magnesium inside red cells - offered by some labs.
The full picture
What is it?
A test of magnesium levels in your blood.
What type of test is it?
A blood biomarker.
What does it measure?
Serum or red-cell magnesium.
Why might someone consider it?
Low magnesium affects muscles, nerves and heart rhythm.
Who is it most relevant for?
People with symptoms or medication risk.
How is it performed?
A blood draw.
How often might it be considered?
When needed.
What can the result help you understand?
Whether magnesium may be low.
What are its limitations?
Serum is insensitive; RBC testing isn’t standardised.
What should it be viewed with?
Potassium, calcium, kidney function and medications.
Where to get it
Through your provider
The simplest route - often covered when there’s a clear reason.
Lab services
e.g. Quest Diagnostics, Labcorp.
Direct-to-consumer panels
e.g. Function Health, InsideTracker.
Names are examples only, not endorsements. Your provider can often order the same test - and help interpret it.
Connected to
Questions to ask your provider
- Could my medicines lower my magnesium?
Ziva Health
One test is a snapshot. Ziva shows the whole story.
Ziva brings your lab results, wearables and daily readings together - and Isabella tells you what’s changing and what to ask your provider next.
Refer Ziva to my provider / care team
Is your provider not on Ziva yet? Send them a link in under a minute - once they join, they’ll see your Magnesium result alongside your other trends and get alerts directly.
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Bring your Ziva 30-day report to your next appointment - your Magnesium result and daily trends in one view, so the conversation starts with the full picture.
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Being listed doesn’t mean everyone needs this test. Educational only — not medical advice. Results should be interpreted with a qualified clinician. ← Back to Know What to Test