The duodenum is usually not visible with a colonoscopy. Gastroscopy allows you to observe the descending part of the duodenum, and for a full duodenal examination, you can choose capsule endoscopy, small boweloscopy, or small bowel CT angiography. A colonoscope enters the rectum through the anus and up to the large intestine, allowing the doctor to look inside the colon and rectum. Colonoscopy is a diagnostic modality used by doctors to examine the inside of the colon and rectum for lesions. Duodenitis may have symptoms such as upper abdominal pain, nausea and vomiting, and in severe cases, vomiting blood and black stools. The duodenum is an integral part of the upper gastrointestinal tract. Examination of the duodenum can be done by capsule endoscopy, small bowel microscopy, or CT imaging of the small bowel. Angiography may be considered for duodenal bleeding in areas below the descending segment of the duodenum. The different examination programs need to choose the appropriate examination according to the different causes of the disease. It is recommended to keep a good attitude and actively cooperate with the doctor, please follow the doctor’s instructions.