In diagnosing IBS, it’s important to identify all the symptoms present, particularly any “red flags”. Doctors will also need to consider alternative diagnoses for IBS, especially for symptoms that may be shared with other diseases. There are a variety of test that can be used when diagnosing IBS; IBS Symptom History, Physical Exam, Stool Analysis, Blood Tests, Lactose Intolerance Test, Breath Tests, Lower GI Series, Colonoscopy and Sigmoidoscopy, and CT Scan are a few.