Hypomagnesemia (low serum magnesium) is very common in critically unwell patients but can occur in the community, particularly secondary to medication use. Magnesium has a vital role in membrane stabilization and while the symptoms of mild deficiency can be nonspecific, severe hypomagnesemia can cause serious complications, such as cardiac arrhythmias and seizures. Hypomagnesemia is commonly seen alongside other electrolyte abnormalities, and magnesium levels should always be checked in patients with hypokalemia or hypocalcemia. Management consists of magnesium replacement, treatment of associated electrolyte imbalances, and addressing the underlying causes.
|Causes of hypomagnesemia|
- Gastrointestinal: anorexia, nausea, vomiting
- Cardiac 
- Metabolic disturbances
- Repletion should be considered in all patients with symptoms consistent with hypomagnesemia, including patients with normal serum magnesium levels. 
- See “ .”
- Identify and treat concurrent electrolyte abnormalities, particularly hypokalemia and hypocalcemia. 
- Identify and treat the underlying cause (see causes of hypomagnesemia).
- Consider continuous cardiac monitoring. 
Special patient groups
Neonatal hypomagnesemia 
- Definition: low serum magnesium levels in a newborn
- Risk factors
- Pathophysiology: maternal hyperglycemia → abnormal maternal calcium-phosphorus metabolism → ↑ maternal urinary Mg excretion → maternal hypomagnesemia → fetal hypomagnesemia → impaired PTH synthesis in the fetus → fetal hypocalcemia and hypomagnesemia
- Clinical features
- Diagnostics: serum magnesium level < 1.6 mg/dL
- Treatment: IV magnesium for symptomatic patients
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