A 52-year-old man with a 15-year history of alcohol use disorder presents with jaundice, ascites, and spider angiomas. Clinical examination reveals hepatomegaly and splenomegaly. Serum bilirubin is 4.2 mg/dL, AST 120 U/L, ALT 65 U/L, and albumin 2.8 g/dL. Which investigation is most appropriate to confirm the diagnosis of cirrhosis and assess its etiology?