Magnesium (Mg)
BMP / ElectrolytesNormal range
1.3–2.1 mEq/L
SI: 0.65–1.05 mmol/L
Critical low: < 0.5 mEq/L · Critical high: > 3 mEq/L
☎ When to call
Mg < 1.0 with symptoms or on a patient with arrhythmia; on OB mag drips — absent reflexes or RR < 12 means stop the infusion and call.
What you do
- Low Mg keeps K and Ca low — replace Mg first or the others won't stick
- Low: watch for tremors, hyperreflexia, torsades risk — telemetry
- On a mag drip (OB): check reflexes, RR ≥ 12, urine output; keep calcium gluconate available as the antidote
Causes of HIGH magnesium
Causes of LOW magnesium
Source: Pagana, Mosby's Manual of Diagnostic and Laboratory Tests, 7th ed.Reference only — verify against your facility's policy.
