++
For further information, see CMDT Part 21-13: Hypomagnesemia
+++
Essentials of Diagnosis
++
Serum concentration may be normal even in the presence of magnesium depletion
Check urinary magnesium excretion if renal magnesium wasting is suspected
Causes neurologic symptoms and arrhythmias
Impairs release of parathyroid hormone (PTH)
+++
General Considerations
++
Causes of hypomagnesemia are listed in Table 21–10
Normomagnesemia does not exclude magnesium depletion because only 1% of total body magnesium is in the extracellular fluid
Hypomagnesemia and hypokalemia share many etiologies, including
Diuretics
Diarrhea
Alcoholism
Aminoglycosides
Amphotericin
Renal potassium wasting is refractory to potassium replacement until magnesium is repleted
Hypomagnesemia also suppresses PTH release and causes end-organ resistance to PTH and low 1,25-dihydroxyvitamin D3 levels and consequent hypocalcemia is refractory to calcium replacement until the magnesium is normalized
Molecular mechanisms of magnesium wasting have been revealed in some hereditary disorders
++
++
Weakness, muscle cramps
Marked neuromuscular and central nervous system hyperirritability
Hypertension, tachycardia, and ventricular arrhythmias
++
Serum magnesium < 1.8 mg/dL (< 0.75 mmol/L)
Urinary excretion of magnesium exceeding 10–30 mg/day or a fractional excretion more than 2% indicates renal magnesium wasting
Hypokalemia and hypocalcemia are often present
PTH secretion is often suppressed
+++
Diagnostic Procedures
++
++