The main instrument that is used to look inside the colon is the colonoscope, which is a long, thin, flexible tube with a tiny video camera and a light on the end. By adjusting the various controls on the colonoscope, the gastroenterologist can carefully guide the instrument in any direction to look at the inside of the colon. The quality picture from the colonoscope is shown on a TV monitor and gives a clear detailed view. Colonoscopy is more precise than an x-ray. 
 

This procedure also allows other instruments to be passed through the colonoscope. These may be used, for example, to painlessly remove a suspicious-looking growth or to take a biopsy – a small piece for further analysis. In this way, colonoscopy may help to avoid surgery or better define what type of surgery may need to be done.

A shorter version of the colonoscope is called a sigmoidoscope, an instrument used to screen the lower part of the large bowel only. The colonoscope, however, is long enough to inspect all of the large bowel and even part of the small intestine.

More information about the procedure, as well as preparation instructions, can be found in this video:

During the procedure, everything will be done to ensure your comfort. An intravenous, or IV, line will be inserted to give you medication to make you relaxed and drowsy. The drug will enable you to remain awake and cooperative, but it may prevent you from remembering much of the experience.
 

Once you are fully relaxed, your doctor will do a rectal exam with a gloved, lubricated finger; then the lubricated colonoscope will be gently inserted.
 

As the scope is slowly and carefully passed, you may feel as if you need to move your bowels, and because air is introduced to help advance the scope, you may feel some cramping or fullness. Generally, however, there is a little or no discomfort.
 

The time needed for colonoscopy will vary, but on the average, the procedure takes about 30 minutes. Afterwards, you will be cared for in a recovery area until the effects of the medication have worn off. At this time, your doctor will inform you about the results of your colonoscopy and provide any additional information that you need to know. You will also be given instructions about how soon you can eat and drink, plus other guidelines for resuming your normal routine.
 

By the time you are ready to go home, you will feel stronger and more alert. Nevertheless, you should rest for the remainder of the day. It is advised that you have a family member or friend take you home.

Colonoscopy is a safe and effective way to evaluate problems such as blood loss, pain, and changes in bowel habits, such as chronic diarrhea or abnormalities that may have first been detected by other tests. Colonoscopy can also identify and treat active bleeding from the bowel.
 

Colonoscopy is also an important way to check for colon cancer and to treat colon polyps – abnormal growths on the inside lining of the intestine. Polyps vary in size and shape and, while most are not cancerous, some may turn into cancer. However, it is not possible to tell just by looking at a polyp if it is malignant or potentially malignant. This is why colonoscopy is often used to remove polyps, a technique called a polypectomy.
 

Colonoscopy is also used as a screening and surveillance test for patients with a family history of colonic cancer.

Although colonoscopy is a safe procedure, complications can sometimes occur. These include perforation – a puncture of colon walls, which could require surgical repair. When polyp removal or biopsy is performed, hemorrhage (heavy bleeding) may result and sometimes require blood transfusion or reinsertion of the colonoscope to control the bleeding. 

As sedation medications need to be used for the procedure, there are risks associated with the medications used, for example allergic reaction and/or side effects. As with any invasive procedures, there are risks of infections.

Again, these complications are unlikely. Be sure to discuss any specific concerns you may have with your doctor.