Hypomagnesemia
Hypomagnesemia is a serum magnesium level below 1.7 mg/dL, most often caused by gastrointestinal losses, proton pump inhibitors, or renal magnesium wasting from diuretics and other drugs. It causes concurrent hypokalemia and hypocalcemia and can potentiate cardiac arrhythmias, and treatment is intravenous magnesium sulfate for significant symptoms or slow-release oral repletion for milder deficiency.
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What this article covers
- Overview
Low serum magnesium from decreased intake, decreased absorption, or increased loss: hypomagnesemia is defined by a serum magnesium level <1.7 mg/dL (0.7 mmol/L), reflecting decreased gastrointestinal…
- Epidemiology
Affects about 20% of hospitalized patients, making it a common electrolyte disturbance encountered on general medical and surgical services.
- Risk factors
Loop and thiazide diuretics: increase renal magnesium excretion and are among the most common causes of chronic hypomagnesemia.
- Pathophysiology
Two source categories: decreased absorption or increased loss.
- Clinical features
Neuromuscular irritability is the earliest recognizable pattern: tremors and fasciculations appear first, generally once the serum magnesium falls below 1.2 mg/dL (0.5 mmol/L).
- Differential diagnosis
Hypocalcemia from another cause (vitamin D deficiency, hypoparathyroidism): also produces Chvostek and Trousseau signs and carpopedal spasm, but serum magnesium is normal and PTH is appropriately…
- Diagnosis
The diagnosis is confirmed by a serum magnesium level <1.7 mg/dL (0.7 mmol/L), and clinically significant symptoms are expected once the level falls below 1.2 mg/dL (0.5 mmol/L); there is no separate…
- Management
First, identify and remove the offending cause when possible, such as stopping an unnecessary diuretic or PPI, or treating diarrhea, then initiate repletion sized to severity.
- Complications
Ventricular arrhythmia, including torsade de pointes: the most life-threatening consequence, particularly with concurrent hypokalemia, ischemia, or QT-prolonging drugs.
- Prognosis
Excellent with identification and correction of the underlying cause: most cases, including PPI-induced hypomagnesemia, resolve rapidly once the offending drug or process is stopped and magnesium is repleted.
- Prevention
Check magnesium level periodically in patients on chronic loop or thiazide diuretics, particularly when hypokalemia is also present, and supplement with oral magnesium oxide 400-800 mg PO daily if levels trend low.
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Related articles
- Hypocalcemia
Hypocalcemia is a low serum calcium concentration, most often from insufficient parathyroid hormone action (postsurgical or autoimmune hypoparathyroidism, hypomagnesemia, or PTH resistance) or from vitamin D deficiency and chronic kidney disease. Severe or symptomatic disease requires urgent intravenous calcium, while chronic disease is managed with oral calcium, vitamin D repletion, and calcitriol when PTH is absent or the kidney cannot activate vitamin D.
- Hypermagnesemia
Hypermagnesemia is a serum magnesium level above 2.4 mg/dL, almost always caused by excess magnesium intake in the setting of reduced kidney function. Mild cases are managed by stopping magnesium sources and enhancing renal excretion, while symptomatic disease needs immediate intravenous calcium gluconate followed by hemodialysis.
- Acute kidney injury
Acute kidney injury is a sudden rise in serum creatinine or fall in urine output from prerenal, intrinsic, or postrenal causes, defined and staged by KDIGO criteria. Management targets the underlying cause, corrects volume and electrolyte derangements, and escalates to renal replacement therapy for refractory hyperkalemia, acidosis, volume overload, or uremia.