Which statement about SIADH is true?

Which statement about SIADH is true?

• A. Too little ADH causes water retention.
• B. Too much ADH causes water retention and dilutional hyponatremia.
• C. ADH is secreted by lung cancer cells.
• D. It causes dehydration.

Answer: (B)

Excess ADH drives the kidneys to reabsorb more free water, which lowers serum osmolality and dilutes the bloodstream. In SIADH, this ADH secretion happens inappropriately, so even though the body is already getting water, the kidneys keep holding onto it. The result is dilutional hyponatremia, with a low serum sodium and a low serum osmolality, while the urine remains inappropriately concentrated (high urine osmolality) and often has a high urine sodium. Because the body isn’t losing water, you don’t see dehydration; patients are typically euvolemic or slightly fluid-overloaded rather than volume-depleted. So the best statement is that too much ADH causes water retention and dilutional hyponatremia. In SIADH, this is the mechanism behind the low sodium and the concentrated urine. Clinically, you’d expect low serum sodium, low plasma osmolality, high urine osmolality, and status that is not dehydration. Management focuses on fluid restriction and treating the underlying cause; severe cases may require careful correction of sodium, sometimes with hypertonic saline.

Excess ADH drives the kidneys to reabsorb more free water, which lowers serum osmolality and dilutes the bloodstream. In SIADH, this ADH secretion happens inappropriately, so even though the body is already getting water, the kidneys keep holding onto it. The result is dilutional hyponatremia, with a low serum sodium and a low serum osmolality, while the urine remains inappropriately concentrated (high urine osmolality) and often has a high urine sodium. Because the body isn’t losing water, you don’t see dehydration; patients are typically euvolemic or slightly fluid-overloaded rather than volume-depleted.

So the best statement is that too much ADH causes water retention and dilutional hyponatremia. In SIADH, this is the mechanism behind the low sodium and the concentrated urine. Clinically, you’d expect low serum sodium, low plasma osmolality, high urine osmolality, and status that is not dehydration. Management focuses on fluid restriction and treating the underlying cause; severe cases may require careful correction of sodium, sometimes with hypertonic saline.