II. Precautions
- Serum Magnesium represents only 1 to 1.5% of total body Magnesium (of which only 50% is active, ionized)
- Magnesium levels tend to vary widely (e.g. with respiration) and single values are unlikely to be useful
-
Serum Potassium tends to be a surrogate marker for Serum Magnesium
- Hyperkalemia is typically accompanied by hpermagnesemia
- Hypokalemia is typically accompanied by Hypomagnesemia
- Consider empiric Magnesium Replacement at the time of Potassium Replacement
III. Labs
- Ionized Magnesium is most accurate but is not widely available
- Serum Magnesium
- Normal: 1.8 - 3.0 mg/dl
IV. Causes: Abnormal
- Serum Magnesium >3.0 mg/dl
- See Hypermagnesemia
- Serum Magnesium <1.8 mg/dl
- See Hypomagnesemia
V. References
- Orman and Slovis in Herbert (2018) EM:Rap 18(8): 13-4