Which finding indicates diabetes insipidus in a craniotomy patient?

Which finding indicates diabetes insipidus in a craniotomy patient?

• A. Increased urine output
• B. Decreased urine output
• C. Decreased serum osmolality
• D. Hyponatremia

Answer: (A)

In diabetes insipidus, the posterior pituitary doesn’t release enough antidiuretic hormone, so the kidneys can’t concentrate urine. The result is large volumes of dilute urine, so the most telling sign is increased urine output (polyuria). In a craniotomy patient, this post-op DI manifests as a sudden rise in urine volume as ADH is deficient. If you were looking at labs, you’d expect high serum osmolality and possibly hypernatremia, with low urine osmolality and low urine specific gravity. The other options don’t fit DI: decreased urine output isn’t DI, and decreased serum osmolality or hyponatremia suggests an opposite problem like SIADH or water overload.

In diabetes insipidus, the posterior pituitary doesn’t release enough antidiuretic hormone, so the kidneys can’t concentrate urine. The result is large volumes of dilute urine, so the most telling sign is increased urine output (polyuria). In a craniotomy patient, this post-op DI manifests as a sudden rise in urine volume as ADH is deficient.

If you were looking at labs, you’d expect high serum osmolality and possibly hypernatremia, with low urine osmolality and low urine specific gravity. The other options don’t fit DI: decreased urine output isn’t DI, and decreased serum osmolality or hyponatremia suggests an opposite problem like SIADH or water overload.