Diabetes insipidus

A 25-year-old woman presents to her family physician with polydipsia, polyuria, and dehydration. The excessive thirst began shortly after a car accident approximately three years earlier, which resulted in significant blood loss from the head. A routine blood chemistry reveals a serum sodium concentration of 144 mg/dL. If the physician orders a water deprivation test, which of the following laboratory results would most likely confirm a diagnosis of central diabetes insipidus?