Medical conditions that cause visible blood in bowel movements (rectal bleeding) include harmless conditions, such as hemorrhoids (swollen blood vessels in the anus), and more serious conditions, such as colorectal cancer. Tests used to evaluate rectal bleeding include anoscopy, barium enema, flexible sigmoidoscopy, and colonoscopy. Anoscopy uses a small plastic tube to examine the anus. Barium enema involves administrational barium, a white substance, to outline the large intestine on a special x-ray. Flexible sigmoidoscopy uses a fiberoptic instrument to examine the surface of the rectum and lower colon. Colonoscopy uses a similar but longer instrument to look at the entire colon and enables doctors to take samples from suspicious areas for laboratory testing. Because cancer is common in older people, examination of the rectum and colon (large intestine) is widely recommended for any patient older than 45 years of age with rectal bleeding. However, complete examination of the large intestine may not be necessary in patients 25 to 45 years of age with rectal bleeding unless they also have other symptoms.