A 27-year-old man presents with 1 week of nausea, malaise, a…
A 27-year-old man presents with 1 week of nausea, malaise, anorexia, and low-grade fever followed by new-onset jaundice and dark urine. He recently returned from international travel and reports no alcohol use or IV drug use. Laboratory testing shows AST 1,450 U/L, ALT 1,900 U/L, total bilirubin 5.2 mg/dL, and normal INR. Which diagnostic test best confirms the most likely etiology?