A 40-year-old male with a 10-year history of chronic hepatitis B presents with fatigue, weight loss, poor appetite, and occasional discomfort in the liver area. Examination: no scleral icterus, no spider angiomas, liver palpable 1.5 cm below the costal margin with medium consistency and no tenderness, spleen palpable 2 fingerbreadths below the costal margin with medium consistency, no shifting dullness. Normal liver function tests, HBsAg(+), anti-HBe(+), anti-HBc(+). A diagnosis of hepatitis B cirrhosis is suspected. Which test is most helpful to confirm the diagnosis?