Colonoscopy or coloscopy is the endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. It can provide a visual diagnosis (e.g. ulceration, polyps) and grants the opportunity for biopsy or removal of suspected colorectal cancer lesions.
Colonoscopy can remove polyps as small as one millimetre or less. Once polyps are removed, they can be studied with the aid of a microscope to determine if they are precancerous or not. It takes 15 years or fewer for a polyp to turn cancerous.
Colonoscopy is similar to sigmoidoscopy—the difference being related to which parts of the colon each can examine. A colonoscopy allows an examination of the entire colon (1200–1500 mm in length). A sigmoidoscopy allows an examination of the distal portion (about 600 mm) of the colon, which may be sufficient because benefits to cancer survival of colonoscopy have been limited to the detection of lesions in the distal portion of the colon.
The American Cancer Society "Guidelines for the Early Detection of Cancer" recommend, beginning at age 50, both men and women follow one of these testing schedules for screening to find colon polyps and cancer:
Flexible sigmoidoscopy every 5 years
Colonoscopy every 10 years
Double-contrast barium enema every 5 years
CT colonography (virtual colonoscopy) every 5 years
A sigmoidoscopy is often used as a screening procedure for a full colonoscopy, often done in conjunction with a fecal occult blood test (FOBT). About 5% of these screened patients are referred to colonoscopy.
Virtual colonoscopy, which uses 2D and 3D imagery reconstructed from computed tomography (CT) scans or from nuclear magnetic resonance (MR) scans, is also possible, as a totally non-invasive medical test, although it is not standard and still under investigation regarding its diagnostic abilities. Furthermore, virtual colonoscopy does not allow for therapeutic maneuvers such as polyp/tumour removal or biopsy nor visualization of lesions smaller than 5 millimetres. If a growth or polyp is detected using CT colonography, a standard colonoscopy would still need to be performed.
Additionally, surgeons have lately been using the term pouchoscopy to refer to a colonoscopy of the ileo-anal pouch.
The colon must be free of solid matter for the test to be performed properly. For one to three days, the patient is required to follow a low fiber or clear-liquid only diet. Examples of clear fluids are apple juice, chicken and/or beef broth or bouillon, lemon-lime soda, lemonade, sports drink, and water. It is very important that the patient remain hydrated. Sports drinks contain electrolytes which are depleted during the purging of the bowel. Orange juice, prune juice, and milk containing fiber should not be consumed, nor should liquids dyed red, purple, orange, or sometimes brown; however, cola is allowed. In most cases, tea (no milk) or black coffee (no milk) are allowed.
The day before the colonoscopy, the patient is either given a laxative preparation (such as Picosalax, Bisacodyl, phospho soda, sodium picosulfate, or sodium phosphate and/or magnesium citrate) and large quantities of fluid, or whole bowel irrigation is performed using a solution of polyethylene glycol and electrolytes. Often, the procedure involves both a pill-form laxative and a bowel irrigation preparation with the polyethylene glycol powder dissolved into any clear liquid, preferably a sports drink that contains electrolytes.
In this case, a typical procedure regimen then would be as follows: in the morning of the day before the procedure, a 238 g bottle of polyethylene glycol powder should be poured into 64 oz. of the chosen clear liquid, which then should be mixed and refrigerated. Two bisacodyl 5 mg tablets are taken 3 pm; at 5 pm, the patient starts drinking the mixture (approx. 8 oz. each 15-30 min. until finished); at 8 pm, take two bisacodyl 5 mg tablets; continue drinking/hydrating into the evening until bedtime with clear permitted fluids. A common brand name of bisacodyl is Dulcolax, and store brands are available. A common brand name of polyethylene glycol powder is MiraLAX. It may be advisable to schedule the procedure early on a given day so the patient need not go without food and only limited fluids the morning of the procedure on top of having to go through the foregoing preparation procedures the preceding day.
Since the goal of the preparation is to clear the colon of solid matter, the patient should plan to spend the day at home in comfortable surroundings with ready access to toilet facilities. The patient may also want to have at hand moist towelettes or a bidet for cleaning the anus. A soothing salve such as petroleum jelly applied after cleaning the anus will improve patient comfort.
The patient may be asked to skip aspirin and aspirin-like products such as salicylate, ibuprofen, and similar medications for up to ten days before the procedure to avoid the risk of bleeding if a polypectomy is performed during the procedure. A blood test may be performed before the procedure.