Colonoscopy is a procedure used to examine the rectum and the entire colon. The device used is similar to the endoscope used in upper endoscopy, however the scope used to examine the colon is longer to allow for the examination of the entire colon.

Colonoscopy can show irregularity in the mucosa lining the colon; these include inflammation, polyps and ulcers. The procedure is performed for a variety of reasons including changes in bowel habits such as pencil like stools, rectal bleeding (stools with bright red blood or black tarry material), abdominal pain & weight loss. Colonoscopy is also performed for colon cancer screening purposes. This procedure is also performed to localize the site of bleeding in the colon, once identified multiple modalities can be used to stop the bleeding during the procedure.

The test is frequently used to look for polyps and colorectal cancer. Removing polyps before they turn into cancer could prevent the disease and potentially reduce deaths. Scientific evidence shows that more than one-third of deaths from colorectal cancer could be avoided if people aged 50 years and older were screened regularly.  Despite recent advances in screening and treatment for colon cancer, it is still one of the most common cancers among men and women in the United States. Polyps can be removed using the channel in the colonoscopy, and samples of tissue (biopsies) can be taken to evaluate for the presence of pre-cancerous or cancerous cells. Colonoscopy can also be used to control bleeding, remove foreign bodies, and in some cases remove tumors. The test also enables gastroenterologists to check for inflammatory bowel diseases such as ulcerative colitis and Cohn’s disease. Colonoscopy is being used increasingly as a screening tool in both asymptomatic patients and patients at risk for colon cancer.

Before the colonoscopy the patient is sedate either by a nurse working under a doctor’s supervision or an anesthesiologist. During the colonoscopy, patients are asked to lie on their sides with their knees drawn up towards the abdomen. The doctor begins the procedure by inserting a lubricated, gloved finger into the anus to check for any abnormal masses or blockage. The colonoscope is then well lubricated and inserted into the anus and gently advanced through the colon. The lining of the intestine is examined through the colonoscope. The physician observes the images on a monitor. Pictures can be taken, printed or saved. During the procedure air is pumped through the colonoscope to help clear the path or open the lumen of the colon. If suspicious growths are observed, biopsy forceps or brushes can be inserted through the colon and tissue samples can be obtained and sent to the pathologist for further examination. Small polyps or inflamed tissue can be removed using instruments passed through the scope. Electrosurgical device or laser system can be used in conjunction with the colonoscope.

After the procedure, the patient is kept under observation until the medications’ effects wear off. The patient has to be driven home and can generally resume a normal diet and usual activities unless otherwise instructed. The patient is advised to drink plenty of fluids to replace those lost by laxatives and fasting. There may be small amounts of blood in the stool for a few days If a biopsy was performed or a polyp was removed, however the physician should immediately be notified if the patient experiences severe abdominal pain or has persistent and heavy bleeding.

For patients with abnormal results such as polyps, the gastroenterologist will recommend another colonoscopy; the timing will depend on a variety of factors such as the size, type and the number of polyps. Risks of the procedures are minimal, however rarely, (2 in 1,000 cases) a perforation (a hole) may occur in the intestinal wall. Heavy bleeding due to the removal of the polyp or from the biopsy site occurs infrequently (one in 1,000 cases). Some patients may have adverse reactions to the sedatives administered during the colonoscopy, but severe reactions are very rare. Infections due to a colonoscopy are also extremely rare.


There are alternatives to colonoscopy including fecal occult blood test, stool DNA test or barium enema. Virtual colonoscopy is a new technique under further development and evaluation for screening for colon polyps and cancer, and is undergoing continual improvement.

Please see the FAQ section for preparation instructions for the procedure.