Which hormone is deficient in central diabetes insipidus?

• A. Thyroid-stimulating hormone.
• B. Growth hormone.
• C. Antidiuretic hormone.
• D. Prolactin.

Answer: (C)

Central diabetes insipidus occurs when there is not enough antidiuretic hormone (ADH) to tell the kidneys to conserve water. ADH normally acts on the kidney’s collecting ducts to increase water reabsorption, which concentrates the urine. When ADH is deficient, the kidneys reabsorb less water, producing large volumes of dilute urine and triggering increased thirst. Among the hormones listed, only antidiuretic hormone is directly involved in this process; thyroid-stimulating hormone, growth hormone, and prolactin regulate other body functions and don’t control water balance in the kidney. So the condition arises from low ADH, while the other hormones aren’t responsible for central diabetes insipidus. To distinguish from nephrogenic diabetes insipidus, note that in central DI ADH is reduced, whereas in nephrogenic DI the kidneys don’t respond to ADH despite its presence.