A 45-year-old male with a 17-year history of chronic hepatitis B reports decreased stamina, occasional abdominal distension, and weight loss over the past year. One week ago, he developed diarrhea and abdominal pain after consuming contaminated food. Diarrhea improved with medication, but fever, severe abdominal pain, distension, yellow urine, and markedly decreased urine output occurred in the last 3 days. On admission: alert but agitated and talkative, chronic liver disease facies, mild icterus of the sclera, prominent palmar erythema, spider angiomas, no abnormalities in heart and lungs; abdominal distension, tenderness in the lower abdomen, mild rebound tenderness, positive ascites sign. Emergency labs: WBC 9.8×10<sup>9</sup>/L (neutrophils 89%), K<sup>+</sup> 3.4 mmol/L, Na<sup>+</sup> 137 mmol/L, Cl<sup>-</sup> 98 mmol/L, blood ammonia 96 μmol/L. The primary basis for diagnosing hepatorenal syndrome (HRS) is: