Which condition is listed as a cause of hypernatremia due to increased intake or retention?

• A. Hyperaldosteronism
• B. Bicarbonate infusion IV excess
• C. Dialysis fluid excess
• D. Severe dehydration

Answer: (A)

Hypernatremia arises when water loss or a failure to match water intake with sodium increases leaves sodium relatively high. When the cause is increased intake or retention of sodium, the driver is excess aldosterone. Hyperaldosteronism raises levels of aldosterone, which boosts sodium reabsorption in the distal nephron through ENaC channels and the Na+/K+ ATPase pump. Water follows this sodium reabsorption osmotically, expanding the extracellular fluid and elevating serum sodium. This situation often comes with potassium loss and can lead to metabolic alkalosis as well. In contrast, bicarbonate infusion mainly alters acid-base balance, dialysis fluid excess depends on dialysate composition and external fluid shifts, and severe dehydration causes hypernatremia by losing water rather than by retaining or gaining sodium.