30th April 2024

A 45-year-old man presents with sudden onset of severe right upper quadrant pain that radiates to his back.

A 45-year-old man presents with sudden onset of severe right upper quadrant pain that radiates to his back. The pain started 2 hours after eating a fatty meal and has been unrelenting since then. He has experienced similar, though less severe, episodes over the past six months. He denies any history of jaundice or changes in the colour of his stool. On examination, he is tender in the right upper quadrant but does not have a fever.

Which investigation is first-line to confirm the diagnosis?