What is a colonoscopy?
Colonoscopy is a procedure used to see inside the colon and rectum. Colonoscopy can detect inflamed
tissue, ulcers, and abnormal growths. The procedure is used to look for early signs of colorectal cancer
and can help doctors diagnose unexplained changes in bowel habits, abdominal pain, bleeding from the
anus, and weight loss
What are the colon and rectum?
The colon and rectum are the two main parts of the large intestine. Although the colon is only one part
of the large intestine, because most of the large intestine consists of colon, the two terms are often used interchangeably. The large intestine is also sometimes called the large bowel.
The colon and rectum are the two main parts of the large intestine.
Digestive waste enters the colon from the small intestine as a semisolid. As waste moves toward the
anus, the colon removes moisture and forms stool. The rectum is about 6 inches long and connects the
colon to the anus. Stool leaves the body through the anus. Muscles and nerves in the rectum and anus
control bowel movements.
How To Prepare For Your Colonoscopy
The doctor usually provides written instructions about how to prepare for colonoscopy. The process is
called a bowel prep. Generally, all solids must be emptied from the gastrointestinal tract by following a
clear liquid diet for 1 to 3 days before the procedure. Patients should not drink beverages containing red
or purple dye. Acceptable liquids include
- fat-free bouillon or broth
- strained fruit juice
- plain coffee
- plain tea
- sports drinks, such as Gatorade
A laxative or an enema may be required the night before colonoscopy. A laxative is medicine that
loosens stool and increases bowel movements. Laxatives are usually swallowed in pill form or as a
powder dissolved in water. An enema is performed by flushing water, or sometimes a mild soap
solution, into the anus using a special wash bottle.
Patients should inform the doctor of all medical conditions and any medications, vitamins, or
supplements taken regularly, including
- arthritis medications
- blood thinners
- diabetes medications
- vitamins that contain iron
Driving is not permitted for 24 hours after colonoscopy to allow the sedative time to wear off. Before
the appointment, patients should make plans for a ride home.
How is colonoscopy performed?
Examination of the Large Intestine
During colonoscopy, patients lie on their left side on an examination table. In most cases, a light
sedative, and possibly pain medication, helps keep patients relaxed. Deeper sedation may be required in
some cases. The doctor and medical staff monitor vital signs and attempt to make patients as
comfortable as possible.
During colonoscopy, patients lie on their left side on an examination table.
The doctor inserts a long, flexible, lighted tube called a colonoscope, or scope, into the anus and slowly
guides it through the rectum and into the colon. The scope inflates the large intestine with carbon
dioxide gas to give the doctor a better view. A small camera mounted on the scope transmits a video
image from inside the large intestine to a computer screen, allowing the doctor to carefully examine the
intestinal lining. The doctor may ask the patient to move periodically so the scope can be adjusted for
Once the scope has reached the opening to the small intestine, it is slowly withdrawn and the lining of
the large intestine is carefully examined again. Bleeding and puncture of the large intestine are possible
but uncommon complications of colonoscopy.
Removal of Polyps and Biopsy
A doctor can remove growths, called polyps, during colonoscopy and later test them in a laboratory for
signs of cancer. Polyps are common in adults and are usually harmless. However, most colorectal
cancer begins as a polyp, so removing polyps early is an effective way to prevent cancer.
The doctor can also take samples from abnormal-looking tissues during colonoscopy. The procedure,
called a biopsy, allows the doctor to later look at the tissue with a microscope for signs of disease.
The doctor removes polyps and takes biopsy tissue using tiny tools passed through the scope. If
bleeding occurs, the doctor can usually stop it with an electrical probe or special medications passed
through the scope. Tissue removal and the treatments to stop bleeding are usually painless.
Colonoscopy usually takes 30 to 60 minutes. Cramping or bloating may occur during the first hour after
the procedure. The sedative takes time to completely wear off. Patients may need to remain at the clinic
for 1 to 2 hours after the procedure. Full recovery is expected by the next day. Discharge instructions
should be carefully read and followed.
Patients who develop any of these rare side effects should contact their doctor immediately:
- severe abdominal pain
- bloody bowel movements
At what age should routine colonoscopy begin?
Routine colonoscopy to look for early signs of cancer should begin at age 50 for most people—earlier if
there is a family history of colorectal cancer, a personal history of inflammatory bowel disease, or other
risk factors. The doctor can advise patients about how often to get a colonoscopy.
Points to Remember
Colonoscopy is a procedure used to see inside the colon and rectum.
- All solids must be emptied from the gastrointestinal tract by following a clear liquid diet for 1 to 3 days before colonoscopy.
- During colonoscopy, a sedative, and possibly pain medication, helps keep patients relaxed.
- A doctor can remove polyps and biopsy abnormal-looking tissues during colonoscopy.
- Driving is not permitted for 24 hours after colonoscopy to allow the sedative time to wear off.
Hope Through Research
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) conducts and supports
basic and clinical research into many digestive disorders. The NIDDK is working to improve
colonoscopy by developing new tools, including tools that improve the ability to detect all colon polyps
and to identify people at increased risk of colorectal cancer. Such tools will help train doctors to
perform colonoscopy, improve safety, and make the procedure more comfortable for patients.