Vitamins & minerals
Magnesium RBC
LOINC 30387-5 · mg/dL
Ranges
Reference range: 4.2–6.8 mg/dL
What it is
RBC magnesium measures magnesium inside red blood cells, which some clinicians use as a fuller picture of magnesium stores than the standard blood test.
Why it matters
Because most magnesium is inside cells, this test can reflect tissue magnesium status more closely.
What high values can mean
A higher value is uncommon and is interpreted in context, often with kidney function.
What low values can mean
A lower value may suggest depleted magnesium stores even when standard blood magnesium looks normal.
How to improve it
Magnesium-rich foods and, when advised, supplements rebuild stores.
Food & lifestyle
Nuts, seeds, legumes, whole grains and leafy greens are rich in magnesium.
Preparing for the test
A blood test; fasting is not usually required — follow your lab's instructions.
When to talk to a doctor
Discuss a low RBC magnesium with a doctor, especially with cramps, fatigue or palpitations.
Related markers
Sources
- NIH Office of Dietary Supplements
- Testing.com (AACC)
Content reviewed on June 26, 2026
Medical disclaimer
This content is for educational purposes only. It is not medical advice and does not diagnose, treat, or prevent any condition. Reference ranges vary between laboratories — always use the range printed on your report and discuss your results with a healthcare professional.
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