BiomarkersRBC magnesium
Minerals
RBC magnesium
Magnesium inside your red blood cells
On your report it may say: Red blood cell magnesium
RBC magnesium measures magnesium inside red cells rather than in the fluid around them. Some doctors use it to judge body stores when serum magnesium looks normal.
Typical ranges · mg/dL
mmol/L = mg/dL × 0.411
Ranges differ between labs; use the one on your report.
Ranges vary by lab, age and sex. The range printed on your report applies.
If it's low
Cell magnesium may be low even if serum looks fine.
Common causes
- Same as low serum magnesium
What you might notice
- Cramps
- Poor sleep
- Tiredness
If it's high
Uncommon; usually linked to kidney issues or high supplement use.
Common causes
- Kidney disease
- High supplement use
What you might notice
- Usually none
Testing
- Who should test
- People with ongoing magnesium-type symptoms and a normal serum result.
- How to prepare
- No fasting needed.
- When to retest
- 3 months after a change.
What can help
Food sources
Discuss with your doctor if you have kidney disease before taking magnesium.
Common questions
Is this test standard?
No, it's a specialised test and not on most panels.
How long to change it?
Several weeks, as red cells turn over slowly.
Explore further
When to take them
Sources
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Build My Nutrition PlanFor general education only, not medical advice. Ranges shown are typical for adults; the range printed on your lab report applies. Talk to a qualified doctor about your results.