A 58-year-old male with a history of decompensated cirrhosis presents with progressive fatigue, abdominal distension, and decreased urine output over the past week. Physical examination reveals tense ascites, bilateral lower extremity edema, and a blood pressure of 90/60 mmHg. Laboratory tests show a serum creatinine of 3.2 mg/dL (baseline 0.8 mg/dL), BUN of 50 mg/dL, and bland urine sediment. Which of the following is the hallmark feature of hepatorenal syndrome (HRS)?
