A 45-year-old woman comes to the physician for a 2-month history of yellow eyes. She had a cholecystectomy performed 12 years ago for acute cholecystitis. Laboratory studies show a direct bilirubin of 1.5 mg/dL and ALP of 200 IU/L. Amylase is 100 U/L. Anti-nuclear antibody titers are negative. Which of the following is the next best step in diagnosis?
Anti-mitochondrial antibodies
CT of the abdomen with contrast
Endoscopic retrograde cholangiopancreatography
Liver biopsy
Ultrasound of the abdomen
