What is SIAD?

What is SIAD?

• A. A disorder caused by excessive aldosterone
• B. A disorder of sodium and water balance caused by the inappropriate release of antidiuretic hormone (ADH)
• C. A disorder of potassium handling
• D. An autoimmune condition

Answer: (B)

SIAD is a disorder of sodium and water balance caused by the inappropriate release of antidiuretic hormone (ADH). Normally ADH raises water reabsorption in the kidneys when plasma osmolality is high or volume is low, concentrating the urine. In SIAD, ADH remains elevated even when plasma osmolality is low, so the kidneys keep reabsorbing water, diluting the blood and leading to hyponatremia with a low serum osmolality. The urine, paradoxically, stays inappropriately concentrated, and the patient is typically euvolemic rather than salt-losing or volume-depleted. This mechanism is distinct from problems caused by excess aldosterone (which alters sodium and water balance via mineralocorticoid effects and often shifts potassium), separate potassium handling disorders, or autoimmune conditions.

SIAD is a disorder of sodium and water balance caused by the inappropriate release of antidiuretic hormone (ADH). Normally ADH raises water reabsorption in the kidneys when plasma osmolality is high or volume is low, concentrating the urine. In SIAD, ADH remains elevated even when plasma osmolality is low, so the kidneys keep reabsorbing water, diluting the blood and leading to hyponatremia with a low serum osmolality. The urine, paradoxically, stays inappropriately concentrated, and the patient is typically euvolemic rather than salt-losing or volume-depleted. This mechanism is distinct from problems caused by excess aldosterone (which alters sodium and water balance via mineralocorticoid effects and often shifts potassium), separate potassium handling disorders, or autoimmune conditions.