Which of the following is NOT listed as a cause of hypomagnesemia?

• A. IV magnesium-deficient therapy
• B. Hyperthyroidism
• C. Hypercalcemia
• D. Renal tubular disorders

Answer: (B)

Magnesium balance is determined by how much is absorbed from the gut and how much is reclaimed by the kidneys. Hypomagnesemia arises when intake or absorption is inadequate, losses are increased, or renal excretion is excessive. If IV therapy is given without magnesium, there’s no external Mg supply, so over time serum magnesium can fall — a direct cause of low Mg. Renal tubular disorders disrupt the kidney’s ability to reclaim magnesium, leading to ongoing urinary losses and low magnesium levels. Hypercalcemia can be associated with hypomagnesemia because high calcium states can affect renal handling and absorption of magnesium, contributing to decreased Mg. Hyperthyroidism, however, does not typically cause hypomagnesemia directly, so it isn’t considered a common or listed cause.