Which condition is described as a hyponatremia cause associated with hypoaldosteronism?

• A. Addison's disease
• B. Ketonuria
• C. Salt losing nephropathy
• D. Prolonged vomiting and diarrhea

Answer: (A)

Hyponatremia due to hypoaldosteronism happens when aldosterone production falls, so the kidneys fail to reabsorb sodium effectively. Aldosterone normally acts on the distal tubules to reclaim Na+ while excreting K+. With reduced aldosterone, more sodium is lost in urine and water follows, lowering serum sodium and often causing volume depletion. Addison's disease is primary adrenal failure that decreases aldosterone (and cortisol), making hyponatremia a common feature.

Other scenarios listed can cause hyponatremia through different mechanisms. Ketosis and ketonuria are metabolic issues not directly tied to aldosterone function. Salt-losing nephropathies cause renal salt loss but describe a kidney problem rather than a hormonal deficiency. Prolonged vomiting and diarrhea reduce body sodium through losses, but the key link here is not hypoaldosteronism.