Colonoscopy is the minimally invasive endoscopic examination of the large colon and the distal part of the small bowel with a fiber optic camera on a flexible tube passed through the anus. It may provide a visual diagnosis (e.g. ulceration, polyps) and grants the opportunity for biopsy of suspected lesions. Virtual colonoscopy, which uses 3D imagery reconstructed from computed tomography scans, is also possible, as a totally non-invasive medical test, although it is not standard and still under investigation.
Indications for colonoscopy include gastrointestinal hemorrhage, unexplained changes in bowel habit or suspicion of malignancy. Colonoscopies are often used to diagnose or rule out colon cancer, but are also frequently used to diagnose inflammatory bowel disease. In older patients (sometimes even younger ones) an unexplained drop in hematocrit (one sign of anemia) is an indication to do a colonoscopy, usually along with an EGD. Even if no obvious blood has been seen in the stool (feces).
Fecal occult blood is a quick test can be done to test for microscopic traces of blood in the stool. A positive test is almost always an indication to do a colonoscopy. In most cases the positive result is just due to hemorrhoids, however it can also be due to polyps (which are easily removed during the colonoscopy procedure), diverticulosis, inflammatory bowel disease (Crohn's disease, ulcerative colitis), or colon cancer.
The days prior to the colonoscopy the patient is given laxatives (e.g. sodium picosulfate) and large quantities of fluid, causing frequent diarrhea or loose stools. (enemas are rarely needed anymore). On the day before the examination, only a light breakfast can be had, after which only clear fluids are permitted until drinking a laxative solution begins (usually around 5:00pm the night before). After that, nothing should be taken by mouth until after the procedure the following day.
During the procedure the patient is often sedated intravenously, employing agents such as midazolam or pethidine (meperidine or Demerol®). The average person will receive a combination of these two drugs, usually between 1-4 mg iv midazolam, and 75 to 125 mg iv pethidine.
The first step is usually a digital rectal examination, to examine the tone of the sphincter and to determine if preparation has been adequate. The endoscope is then passed though the anus up the rectum, the sigmoid colon, the descending, transverse and ascending colon, the caecum, and the terminal ileum. The endoscope has a movable tip and multiple channels for instrumentation, air, suction and light. The bowel is occasionally insufflated with air to maximize visibility.
Suspicious lesions may be cauterized, treated with laser light or cut with an electric wire for purposes of biopsy. Medication can be injected, e.g. to control bleeding lesions. On average, the procedure takes 20-30 minutes, depending on the indication and findings.
After the procedure, some recovery time is usually allowed to let the sedative wear off. Most facilities require that you have a person with you to help get you home afterwards.
A very small proportion suffers a perforation. This is a medical emergency and requires immediate surgery.