What is SIADH?

What is SIADH?

• A. An overproduction of aldosterone causing water retention
• B. A condition characterized by impaired renal excretion of water
• C. A deficiency of ADH causing dehydration
• D. An autoimmune kidney disease

Answer: (B)

SIADH is a situation where antidiuretic hormone is released inappropriately, so the kidneys keep more water than they should. ADH normally adjusts how much water the kidneys reabsorb in the collecting ducts; when ADH is secreted in excess, too much water is reabsorbed, diluting the blood and causing hyponatremia. The hallmark is low serum osmolality with inappropriately concentrated urine (high urine osmolality) and typically euvolemia. This description fits SIADH best because the core issue is the kidney’s reduced ability to excrete free water due to excessive ADH, not excessive aldosterone, or ADH deficiency, or an autoimmune kidney disease.

SIADH is a situation where antidiuretic hormone is released inappropriately, so the kidneys keep more water than they should. ADH normally adjusts how much water the kidneys reabsorb in the collecting ducts; when ADH is secreted in excess, too much water is reabsorbed, diluting the blood and causing hyponatremia. The hallmark is low serum osmolality with inappropriately concentrated urine (high urine osmolality) and typically euvolemia. This description fits SIADH best because the core issue is the kidney’s reduced ability to excrete free water due to excessive ADH, not excessive aldosterone, or ADH deficiency, or an autoimmune kidney disease.