The most appropriate management is empiric treatment for small intestinal bacterial overgrowth (SIBO) with antibiotics. Digestive enzymes and intestinal motility normally limit the growth of excessive bacteria, but SIBO can occur in conditions in which these functions are disrupted, such as the creation of a blind loop. Bacterial metabolism of carbohydrates prior to small-bowel absorption results in symptoms of SIBO (diarrhea, bloating, flatulence, and weight loss). This patient's symptoms of diarrhea, increased gas, bloating, and abdominal discomfort can collectively be explained by the bacterial fermentation of simple carbohydrates in the small bowel from SIBO. Given her presentation, the pretest probability is high enough to justify empiric therapy for SIBO and monitoring of symptoms for a response.

Because SIBO is a very plausible explanation for this patient's diarrhea, performing a colonoscopy would be premature at this time.

A potent antisecretory agent such as omeprazole is indicated for acid-related disorders, and the symptoms reported by this patient are not suggestive of an acid-related disorder. Furthermore, there is some evidence to suggest that the use of a proton pump inhibitor may promote bacterial overgrowth in the small bowel. Therefore, a trial of omeprazole is unlikely to improve this patient's symptoms.

The nature of this patient's abdominal pain is atypical for a biliary source, as it is not meal related or located in the right upper quadrant. Furthermore, this patient's liver chemistry studies were unremarkable and the gallbladder was resected during her gastric bypass surgery. Therefore, the yield of a right upper quadrant ultrasound would be low in this setting.

Stool cultures are generally not helpful in assessing a patient with chronic diarrhea, except if Giardia infection is suspected. In addition, stool cultures are not capable of making the diagnosis of bacterial overgrowth because the bacteria in the blind loop resemble the normal flora of the large bowel. Because this patient's surgical history supports bacterial overgrowth as the cause of diarrhea, an empiric trial of antibiotics is warranted.