A 32-year-old female patient is diagnosed with diabetes insipidus after transsphenoidal resection of a pituitary adenoma. What should the nurse consider as a sign of improvement?

A. Serum sodium of 120 mEq/L
B. Urine specific gravity of 1.001
C. Fasting blood glucose of 80 mg/dL
D. Serum osmolality of 290 mOsm/kg