Review Question - QID 212632

A 53-year-old patient presents to his primary care provider with a 1-week history of abdominal pain at night and between meals. He has attempted taking antacids, which help briefly, but then the pain returns. The patient has not noticed any changes to the color of his stool but states that he has been having some loose bowel movements. The patient reports that he has had duodenal ulcers in the past and is concerned that this is a recurrence. On exam, his temperature is 98.4°F (36.9°C), blood pressure is 130/84 mmHg, pulse is 64/min, and respirations are 12/min. The abdomen is soft, nontender, and nondistended in clinic today. A fecal occult blood test is positive for blood in the stool. During outpatient workup, H. pylori stool antigen is negative, endoscopy demonstrates duodenal ulcers, and gastrin levels are elevated after a secretin stimulation test. Which of the following should also be examined in this patient?