Which of the following statements best describes the clinical features of diabetes insipidus?

• A. Hypernatremia with dehydration and polyuria, with urine osmolality less than 200 mOsm/kg
• B. Hyponatremia with edema and low urine osmolality
• C. Hypokalemia with metabolic acidosis
• D. Hyperkalemia with metabolic acidosis

Answer: (D)

Diabetes insipidus results from a failure to concentrate urine, so free water is lost in large amounts. This drives dehydration and, if water intake doesn’t keep up, hypernatremia. The urine remains very dilute, reflected by a urine osmolality that is markedly low, often less than 200 mOsm/kg.

So the statement that best describes the clinical features is hypernatremia with dehydration and polyuria, with urine osmolality less than 200 mOsm/kg.

Hyponatremia with edema and low urine osmolality points to a different disorder like SIADH, not DI. The ideas of hypokalemia with metabolic acidosis or hyperkalemia with metabolic acidosis describe electrolyte and acid-base disturbances that are not characteristic of DI.