II. Precautions

  1. Serum Magnesium represents only 1 to 1.5% of total body Magnesium (of which only 50% is active, ionized)
  2. Magnesium levels tend to vary widely (e.g. with respiration) and single values are unlikely to be useful
  3. Serum Potassium tends to be a surrogate marker for Serum Magnesium
    1. Hyperkalemia is typically accompanied by hpermagnesemia
    2. Hypokalemia is typically accompanied by Hypomagnesemia
      1. Consider empiric Magnesium Replacement at the time of Potassium Replacement

III. Labs

  1. Ionized Magnesium is most accurate but is not widely available
  2. Serum Magnesium
    1. Normal: 1.8 - 3.0 mg/dl

IV. Causes: Abnormal

  1. Serum Magnesium >3.0 mg/dl
    1. See Hypermagnesemia
  2. Serum Magnesium <1.8 mg/dl
    1. See Hypomagnesemia

V. References

  1. Orman and Slovis in Herbert (2018) EM:Rap 18(8): 13-4

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