Hypermagnesemia can result from which condition?

• A. Decreased excretion by kidneys
• B. Increased urinary excretion
• C. Low magnesium intake
• D. Hypercalciuria

Answer: (A)

Magnesium balance is mainly regulated by the kidneys. Most of the magnesium filtered by the kidneys is excreted in urine, and the kidneys adjust this excretion to match what the body takes in. If the kidneys can’t excrete magnesium effectively—due to renal failure or impaired tubular handling—the excess magnesium stays in the blood, leading to hypermagnesemia.

That’s why decreased excretion by the kidneys is the best explanation. If the body were excreting more magnesium in urine, levels would tend to drop, not rise. A low magnesium intake wouldn’t raise serum magnesium; it would tend to lower it. Hypercalciuria refers to high calcium in urine and does not cause hypermagnesemia.