Which finding would most strongly suggest diabetes insipidus following hypophysectomy?

• A. Increased urine output with low urine specific gravity
• B. Decreased urine output with high urine specific gravity
• C. Elevated serum glucose
• D. Bradycardia

Answer: (A)

Central diabetes insipidus after hypophysectomy arises because ADH (vasopressin) production or release from the posterior pituitary is disrupted. Without ADH, the collecting ducts in the kidney cannot reabsorb water effectively, so a large volume of very dilute urine is produced. That’s why an increased urine output paired with a low urine specific gravity best signals DI in this setting—the urine is dilute even though you’re making a lot of it.

In contrast, urine that is highly concentrated (high specific gravity) would not fit DI; elevated serum glucose would point toward diabetes mellitus with glycosuria as a cause of polyuria; bradycardia isn’t a hallmark finding of DI. So the combination of polyuria with dilute urine specifically points to central DI after hypophysectomy.