The Nurse Caring for a Lung Cancer Patient with Metastasis

The nurse caring for a lung cancer patient with metastasis to the brain suspects the patient has developed a paraneoplastic syndrome known as syndrome of inappropriate antidiuretic hormone (SIADH) secretion. Which laboratory result in this patient who has gained 3 lb in a day would alert the nurse to the possibility of SIADH?

A) Serum potassium of 5.0 mmol/L
B) Serum sodium of 115 mmol/L
C) BUN of 8 mg/dL
D) Hematocrit of 40%