Which finding indicates Diabetes Insipidus in a head injury patient?

Which finding indicates Diabetes Insipidus in a head injury patient?

• A. Urine output 150 mL/hr
• B. Urine output low with high osmolality
• C. Urine output 650 mL/hr
• D. Hypernatremia with low urine output

Answer: (C)

When head injury leads to diabetes insipidus, there’s not enough antidiuretic hormone to help the kidneys concentrate urine. The result is polyuria with dilute urine—you’re losing a lot of water in urine. A urine output as high as 650 mL per hour is a classic sign of this polyuria, fitting the pattern of DI after CNS injury. Consider the other patterns: very low urine output with high urine osmolality means concentrated urine, not DI. A urine output 150 mL/hour is not polyuric enough to suggest DI. Hypernatremia can occur with DI, but that usually accompanies high urine output, not low. So the key clue here is the markedly high urine flow indicating inability to concentrate urine, consistent with diabetes insipidus.

When head injury leads to diabetes insipidus, there’s not enough antidiuretic hormone to help the kidneys concentrate urine. The result is polyuria with dilute urine—you’re losing a lot of water in urine. A urine output as high as 650 mL per hour is a classic sign of this polyuria, fitting the pattern of DI after CNS injury.

Consider the other patterns: very low urine output with high urine osmolality means concentrated urine, not DI. A urine output 150 mL/hour is not polyuric enough to suggest DI. Hypernatremia can occur with DI, but that usually accompanies high urine output, not low. So the key clue here is the markedly high urine flow indicating inability to concentrate urine, consistent with diabetes insipidus.