Diabetes insipidus results from deficiency or resistance to which hormone?

• A. Insulin
• B. Cortisol
• C. Antidiuretic hormone (ADH)
• D. Glucagon

Answer: (C)

Antidiuretic hormone controls water reabsorption in the kidneys. When ADH is present, the collecting ducts become permeable to water, allowing it to be reabsorbed back into the bloodstream and urine becomes concentrated. Diabetes insipidus occurs when there is either a deficiency of ADH production (central DI) or the kidneys don’t respond to ADH (nephrogenic DI). Without adequate ADH action, the collecting ducts don’t reabsorb water effectively, so very large volumes of dilute urine are produced, which can lead to dehydration and increased thirst. Lab clues include high serum osmolality with low urine osmolality. The other hormones listed—insulin, cortisol, and glucagon—don’t regulate kidney water reabsorption and are tied to glucose metabolism or stress response, not DI. The hormone involved in DI is ADH.