Magnesium Imbalances

Magnesium supports neuromuscular transmission, cardiac conduction, membrane stability, and parathyroid hormone secretion and action. Most magnesium is stored inside cells and in bone; less than about 1% of total body magnesium is in extracellular fluid. The serum value therefore samples only a small compartment. A patient can have depleted intracellular stores even when the reported serum magnesium is within the laboratory reference range. The clinical pattern matters as much as the number. Low magnesium generally makes nerves and cardiac tissue more excitable. High magnesium progressively depresses reflexes, conduction, level of consciousness, and breathing. Renal function changes the risk in both directions: renal wasting can produce deficiency, while reduced clearance can make an administered dose accumulate.