RBC magnesium optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for RBC magnesium:
- Optimal 5.5 – 6.8 mg/dL (2.3 – 2.65 mmol/L); sufficient 4.2 – 7.5 mg/dL (1.65 – 3.05 mmol/L); out of range below 4.2 or above 7.5 mg/dL.
Evidence grade: Functional / longevity target. A narrower target in common use in functional, integrative, preventive and longevity practice. It is not a universally validated diagnostic range.
At Sera's last range review a change to this band was proposed and held, because the evidence for it was thin, so the band is unchanged. The note below says where it matches published intervals and where it does not.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| mg/dL | 5.5 – 6.8 | 4.2 – 7.5 | below 4.2 or above 7.5 |
| mmol/L | 2.3 – 2.65 | 1.65 – 3.05 | below 1.65 or above 3.05 |
What the evidence says
Only one laboratory interval could be confirmed, Labcorp's 3.7 to 7.0 mg/dL, and Sera's acceptable band of 4.2 to 7.5 does not match it. The optimal band of 5.5 to 6.8 is a functional-practice convention with no primary source. Red cell magnesium is offered by few laboratories, and at least one large one has withdrawn it.
Assay: Results differ meaningfully between platforms and methods. Compare against the interval printed by the issuing laboratory before acting on a borderline value.
Sources
- Magnesium, RBC — Labcorp Test Directory, 2026 · Laboratory / reference-interval sourceReference interval for red-cell magnesium is 3.7 to 7.0 mg/dL. Sera's sufficient band of 4.2 to 7.5 differs on both sides. Current directory entry, opened October 2026.
What Magnesium (RBC) measures
Magnesium measured inside your red blood cells, which is more accurate than the serum test.
Magnesium drives more than 300 enzyme reactions, energy production, and the nervous system. RBC magnesium aims at the magnesium held inside cells, which a serum test can miss — but read it alongside serum magnesium rather than instead of it: the method is not standardised between laboratories, and the evidence that it outperforms serum magnesium is thinner than its reputation suggests.