Which statement about SIADH is true?

Which statement about SIADH is true?

• A. It causes hypernatremia
• B. It causes hyponatremia due to dehydration
• C. It does not affect aldosterone
• D. It results in dilutional hyponatremia due to increased total body water

Answer: (D)

SIADH is driven by excess ADH causing the kidneys to reabsorb free water. This increases total body water while sodium content stays the same, so serum sodium becomes diluted, leading to dilutional hyponatremia. The condition is typically euvolemic, not dehydrated or hypernatremic, which is why the description of hyponatremia due to water retention fits best. The key feature isn’t a change in aldosterone, but the disproportionate rise in free water relative to sodium. Thus, dilutional hyponatremia from increased total body water best describes SIADH.

SIADH is driven by excess ADH causing the kidneys to reabsorb free water. This increases total body water while sodium content stays the same, so serum sodium becomes diluted, leading to dilutional hyponatremia. The condition is typically euvolemic, not dehydrated or hypernatremic, which is why the description of hyponatremia due to water retention fits best. The key feature isn’t a change in aldosterone, but the disproportionate rise in free water relative to sodium. Thus, dilutional hyponatremia from increased total body water best describes SIADH.