A colonoscopy is a test that doctors perform using a thin, flexible tube called a colonoscope that examines the inner lining of a patient's large intestine. Doctors perform colonoscopies to detect ulcers, polyps and tumors in the colon. Additionally, colonoscopies are used to screen for colon cancer, states WebMD.
A colonoscopy is preceded by a colon prep that lasts one to two days and involves the patient ingesting a liquid medication that induces frequent bowel movements and cleans out the colon in preparation for the test. A doctor then performs a colonoscopy by inserting a colonoscope with a small video camera attachment that takes pictures or videos of the large intestine. During a colonoscopy, the doctor may collect tissue samples for biopsy and remove abnormal growths, reports WebMD.