Normal Magnesium Levels in Blood
The normal serum magnesium range for adults is 0.75-0.95 mmol/L (1.82-2.31 mg/dL), though evidence-based medicine suggests the lower limit should be raised to 0.85 mmol/L (2.07 mg/dL) to prevent health risks associated with chronic latent deficiency. 1, 2
Standard Reference Ranges by Population
Adults
- Traditional reference range: 0.75-0.95 mmol/L (1.82-2.31 mg/dL) 1
- Evidence-based lower limit: 0.85 mmol/L (2.07 mg/dL) is recommended because values below this threshold are associated with increased health risks including type 2 diabetes and cardiovascular disease 1, 2
- Normal range also cited as 1.7-2.3 mg/dL (0.75-0.95 mmol/L) across all ages 3
Neonates and Premature Infants
- Significantly higher than adults: 0.7-1.5 mmol/L during the first two weeks of life 4
- This elevated range reflects the physiological differences in newborns and should not be interpreted using adult reference values 4
- Infants exposed to maternal magnesium sulfate therapy (for preeclampsia or tocolysis) may have even higher levels initially and require individualized monitoring 4
Critical Thresholds for Clinical Action
Hypomagnesemia
- Defined as: <1.8 mg/dL (<0.74 mmol/L) 5
- Severe deficiency: <1.2 mg/dL, at which point symptoms typically manifest 5
- Critical level: <0.60 mmol/L occurs only in patients with known disorders causing magnesium deficiency 6
Hypermagnesemia
- Defined as: >1.00 mmol/L 6
- Mild hypermagnesemia: <1.20 mmol/L typically does not require specific treatment 6
- Most cases occur in renal insufficiency, particularly when creatinine exceeds 0.20 mmol/L 6
Important Clinical Caveats
Serum magnesium is a poor indicator of total body magnesium status because less than 1% of total body magnesium is in blood, with the majority stored intracellularly (particularly in red blood cells at ~2.5 mmol/L) and in bone 4. A normal serum level does not rule out tissue deficiency, as the body maintains serum concentrations by releasing magnesium from bone stores 1, 2.
Key Considerations:
- About one-third of serum magnesium is protein-bound, while two-thirds is filterable by the kidney 4
- Red blood cell magnesium concentration (~2.5 mmol/L) is a better indicator of tissue magnesium content than serum levels 4
- Ionized magnesium is the biologically active fraction, though total serum magnesium is what is routinely measured 4
- The kidney can excrete up to 97% of filtered magnesium, making hypermagnesemia rare except in renal failure 3