Which of the following can cause hyponatremia?

• A. Diabetes insipidus
• B. Hyperglycemia
• C. Hyperaldosteronism
• D. Thiazide diuretic use

Answer: (C)

Hyponatremia happens when there is more free water relative to sodium in the extracellular fluid, so the sodium concentration falls. Thiazide diuretics are a classic cause because they reduce sodium reabsorption in the distal tubule, which can lead to mild volume depletion that stimulates antidiuretic hormone release and increases water reabsorption in the collecting ducts. The result is more water than sodium in the body, diluting serum sodium.

Other options don’t fit as well: diabetes insipidus typically causes water loss and hypernatremia; hyperaldosteronism promotes sodium retention and often hypernatremia; hyperglycemia can cause a dilutional hyponatremia due to osmotic movement of water into the extracellular space, but it’s a dilution effect tied to glucose levels rather than a primary diuretic effect.