Which statement best describes SIADH?

Which statement best describes SIADH?

• A. High antidiuretic hormone production leading to water retention and dilutional hyponatremia
• B. Low antidiuretic hormone production leading to dehydration
• C. Increased aldosterone production causing sodium retention
• D. Decreased serum osmolality due to dehydration

Answer: (A)

SIADH is defined by excess antidiuretic hormone causing the kidneys to reabsorb water, which dilutes the blood and lowers serum sodium (dilutional hyponatremia) while the urine remains concentrated. That’s why the statement about high ADH production leading to water retention and dilutional hyponatremia best describes SIADH. Why the other ideas don’t fit: low ADH would cause excessive urination and dehydration (diabetes insipidus), not water retention. Increased aldosterone promotes sodium and water retention but tends toward hypernatremia rather than hyponatremia. Dehydration raises serum osmolality, not decreases it, so decreased serum osmolality due to dehydration isn’t correct.

SIADH is defined by excess antidiuretic hormone causing the kidneys to reabsorb water, which dilutes the blood and lowers serum sodium (dilutional hyponatremia) while the urine remains concentrated. That’s why the statement about high ADH production leading to water retention and dilutional hyponatremia best describes SIADH.

Why the other ideas don’t fit: low ADH would cause excessive urination and dehydration (diabetes insipidus), not water retention. Increased aldosterone promotes sodium and water retention but tends toward hypernatremia rather than hyponatremia. Dehydration raises serum osmolality, not decreases it, so decreased serum osmolality due to dehydration isn’t correct.