The most appropriate management is reassurance and patient education that addresses the diagnosis and treatment of irritable bowel syndrome (IBS). The American College of Gastroenterology recommends a simple definition of IBS: abdominal pain or discomfort that occurs in association with altered bowel habits over a period of at least 3 months. The diagnosis of IBS is further subtyped into diarrhea predominant (IBS-D), constipation predominant (IBS-C), or mixed (IBS-M), which alternates between diarrhea and constipation. This young woman has symptoms that fulfill diagnostic criteria for IBS-C in the absence of any alarm features. A recent evidence-based review by the American College of Gastroenterology IBS task force concluded that, in such a setting, no further biochemical or structural testing is indicated given the low yield of testing. The routine pursuit of a complete blood count, serum chemistry studies, thyroid function studies, stool studies for ova and parasites, and abdominal imaging is unnecessary in this setting. An essential initial step in management of IBS is the clear establishment of the diagnosis with explanation of and reassurance regarding the patient's symptoms. In addition to reassurance, over-the-counter remedies addressing constipation or diarrheal symptoms can be recommended, as these agents are safe and potentially effective. In this patient, the osmotic laxative polyethylene glycol is likely to be well tolerated and to improve this patient's constipation symptoms.

This patient has no symptoms of diarrhea or blood in the stool, and there is no family history of colon cancer to justify a colonoscopy. The passage of mucus is commonly reported in IBS, so this symptom alone does not warrant colonoscopy.

The typical features of celiac disease are diarrhea, bloating, and weight loss. A tissue transglutaminase serologic study would be a reasonable screening test for celiac disease in a patient with IBS-D, but it is not necessary in patients with IBS-C.