What clinical presentation does SIADH cause?

What clinical presentation does SIADH cause?

• A. Hypernatremia
• B. Hypokalemia
• C. Elevated serum osmolality
• D. Dilutional hyponatremia due to increased total body water

Answer: (D)

SIADH causes dilutional hyponatremia by retaining water through inappropriately elevated ADH, which increases total body water without a proportional rise in sodium. This lowers serum sodium and serum osmolality while the urine remains inappropriately concentrated with higher urine sodium. Clinically, patients are often euvolemic. So the characteristic presentation is hyponatremia due to increased total body water (dilutional hyponatremia), not hypernatremia or a hyperosmolar state. Potassium changes are not the defining feature.

SIADH causes dilutional hyponatremia by retaining water through inappropriately elevated ADH, which increases total body water without a proportional rise in sodium. This lowers serum sodium and serum osmolality while the urine remains inappropriately concentrated with higher urine sodium. Clinically, patients are often euvolemic. So the characteristic presentation is hyponatremia due to increased total body water (dilutional hyponatremia), not hypernatremia or a hyperosmolar state. Potassium changes are not the defining feature.