The most frequent cause of hypermagnesemia is due to

• A. Renal failure
• B. Increased intake of magnesium
• C. Hypoaldosteronism
• D. Acidosis

Answer: (A)

Magnesium balance is governed mainly by renal excretion. The kidneys filter magnesium and then excrete most of what isn’t needed, adjusting loss to keep serum levels in a tight range. When kidney function declines, the ability to remove magnesium diminishes, so magnesium accumulates in the blood. This makes renal failure the most frequent cause of hypermagnesemia, especially in patients with chronic kidney disease or those receiving magnesium-containing medications or IV fluids.

Increasing intake can raise magnesium levels, but only if renal excretion is impaired; with normal kidney function, excess magnesium is typically cleared. Conditions like hypoaldosteronism or acidosis can influence electrolyte balance in other ways, but they do not commonly and primarily drive hypermagnesemia.