A 45-year-old male with a 15-year history of gastric ulcers has experienced loss of abdominal pain rhythmicity in the past 2 months, with poor response to antacid therapy. Which of the following tests is most valuable for definitive diagnosis?
A 45-year-old male with a 15-year history of gastric ulcers has experienced loss of abdominal pain rhythmicity in the past 2 months, with poor response to antacid therapy. Which of the following tests is most valuable for definitive diagnosis?