Magnesium — Normal Range & Interpretation

Clinical Context

Magnesium is an intracellular cation essential for neuromuscular conduction, cardiac rhythm stability, and over 300 enzymatic reactions including ATP metabolism. Serum levels reflect only about 1% of total body magnesium, so normal values do not rule out depletion. Magnesium works closely with potassium and calcium, and imbalances in one often drive imbalances in the others.

Hypomagnesemia results from loop and thiazide diuretics, proton pump inhibitors, chronic alcohol use, malabsorption, diarrhea, and refeeding syndrome. It presents with tremor, tetany, seizures, and torsades de pointes, and it causes refractory hypokalemia and hypocalcemia until magnesium is replaced. Hypermagnesemia occurs in renal failure, excessive magnesium-containing antacids or laxatives, and obstetric magnesium sulfate therapy, producing hyporeflexia, hypotension, and respiratory depression.

High-yield for NP boards: unexplained refractory hypokalemia requires magnesium replacement before potassium will correct. Expect questions linking chronic PPI or diuretic use to low magnesium, and scenarios pairing alcohol use disorder with low magnesium and seizures. Boards also test the classic presentation of torsades de pointes treated with IV magnesium sulfate, and the obstetric patient on magnesium drip who develops absent deep tendon reflexes, signaling toxicity that requires stopping the infusion and administering calcium gluconate.

Related Labs

• HbA1c — %
• ESR — mm/hr
• CRP — mg/dL
• hs-CRP — mg/L
• Uric Acid — mg/dL

Sources

• MedlinePlus