GI endoscopy is a powerful tool for diagnosis of diseases of the digestive tract, and there are a variety of reasons for endoscopic examination of the digestive tract. 

A physician may want to use GI endoscopy to investigate a symptom (a complaint that concerns the patient such as pain, nausea, difficulty swallowing, bleeding or a recent change in bowel habit), a physical finding (an abnormality such as tenderness, a mass or signs of nutritional deficiency found by the physician on physical examination), or a laboratory finding (such as anemia, a low blood count). 

A physician may also recommend GI endoscopy because of his/her concern that a patient is at increased risk of certain disorders due to family history or the patient’s past history. 

Finally, GI endoscopy may be utilized as a screening procedure for patients at average risk for a common disease, especially colorectal cancer.  Since the great majority of colorectal cancers form from a benign growth or polyp of the type called adenoma, screening is done to find those individuals who are forming adenomas.  Since colonoscopy is the most effective way to find adenomas, and it permits removal of any polyp suspicious for adenoma, it is favored by many physicians over a more limited endoscopic examination (flexible sigmoidoscopy), colon x-ray (barium enema) or chemical testing for invisible traces of blood in the stool (fecal occult blood testing).