A colonoscopy is an examination of the entire large intestine (colon and rectum) with a long, thin tube and attached video camera. It is often performed to screen for colorectal cancer, but may also be used to screen for and diagnose other abnormalities, such as inflammatory digestive diseases. Polyps, ulcers, pouches (diverticulosis) and narrowed areas (strictures) can all be detected during a colonoscopy. Some abnormal growths, such as polyps, can also be removed during the procedure.

The examination is performed with a lighted instrument called a colonoscope that is inserted into a patient’s rectum. The success of a colonoscopy depends greatly on a patient’s willingness to follow instructions for cleaning out the colon prior to the procedure. This is necessary to enable the physician to obtain a clear view of the colon’s interior lining.

A physician may recommend a colonoscopy if other screening tests indicate the potential presence of abnormalities in the colon. In addition, the American Cancer Society recommends colonoscopies for all men and women beginning at age 50 and every 10 years thereafter. Individuals with a higher risk for colorectal cancer may require the procedure at an earlier age or more often. However, due to patient modesty and fear of undergoing a colonoscopy, many individuals do not receive this life–saving test. It is estimated that only about half of eligible persons avail themselves of screening for colon cancer.

A colonoscopy is a visual examination of the rectum and the entire colon with a thin, flexible tube attached to a lighted video camera (colonoscope). It is the most sensitive test for diagnosing certain conditions, such as polyps, ulcers, pouches (diverticulosis) and narrowed areas (strictures). It is also used to detect colorectal abnormalities such as precancerous and cancerous growths

The colon is another term for the large intestine, the last portion of the digestive tract, which also includes the esophagus, stomach and the small intestine. The colon measures approximately 3 to 5 feet long (0.91 to 1.52 meters). It starts at the cecum (attached to the end of the small intestine) and ends at the rectum and anus. The colon’s most important job is to dry, process and store food products that are not absorbed into the body. Eventually, this waste is eliminated during defecation.

Colonoscopies capture images that are more sensitive than those provided by x-rays. In addition, colonoscopies can be used for treatment as well as diagnosis for some conditions. For example, in a patient with polyps, a physician can pass surgical instruments through a colonoscope to remove growths that can then be analyzed by a pathologist.

A colonoscopy may be used to diagnose many different disorders of the colon and rectum. A physician may recommend the test if other screening tests indicate a potential problem. These screening tests include a digital rectal examination (during which a physician examines the rectum with a gloved finger), a fecal occult blood test (FOBT) and a barium enema.

A colonoscopy can be used to:

• Identify the location or cause of bleeding in the colon
  
  
• Check for areas of irritation or sores in the colon
  
  
• Diagnose any inflammatory digestive diseases, such as Crohn's disease or ulcerative colitis, that cause symptoms including pain, bloody diarrhea and weight loss
  
  
• Help determine the cause of unexplained changes in weight or bowel habits (e.g., diarrhea)

However, colonoscopies are used most often as a screening tool for colorectal cancer. The American Cancer Society (ACS) recommends that beginning at age 50, all men and women should participate in at least one of the five following screening options:

• Yearly fecal occult blood test (FOBT) or fecal immunochemical test (FIT)
  
  
• Flexible sigmoidoscopy every five years
  
  
• Combination of yearly FOBT/FIT and flexible sigmoidoscopy every five years (preferred by ACS)
  
  
• Double contrast barium enema every five years
  
  
• Colonoscopy every 10 years

In addition, patients younger than 50 with a higher risk of colon cancer should consider a colonoscopy or alternate form of colorectal screening test. This group may include individuals with a family history of colorectal cancer or patients who have been previously treated for colon polyps. It may also include patients who have been diagnosed with another form of cancer. Research also suggests that people who smoke cigarettes and drink heavily may benefit from earlier screening as they often develop colorectal cancer at a younger age than those who refrain from using these substances. 

Colonoscopies present little risk or discomfort to the patient.  However, the success of a colonoscopy largely depends on the patient’s willingness to follow a physician’s instructions on cleaning out the colon prior to the procedure. This may include the use of laxatives or enemas that some patients find uncomfortable or disruptive.

Research indicates that many Americans over the age of 50 fail to receive regular colonoscopies. In fact, a recent study in the United States found that nearly half of over 21,000 patients seen by primary care physicians did not receive a colorectal screening even though it was recommended.

Despite the inconvenience and discomfort, colonoscopies continue to be the best technique for detecting colorectal abnormalities and saving lives.

A newer version of the procedure, called virtual colonoscopy (VC), uses a CAT scan or MRI with computer software to create very detailed x-ray images of the colon and rectum. The test is less invasive than a traditional colonoscopy but has limitations. VC is not as detailed as conventional colonoscopy and may miss small polyps. Also, if a polyp is found with VC, a conventional colonoscopy is still necessary to remove the growth. Studies comparing the two techniques to more traditional colonoscopies have yielded mixed results. The technology is improving, and virtual colonoscopies show promise for the future. However, at this time, the ACS does not recommend VC as a screening tool for early detection of colorectal cancer. VC requires the same pre-procedure colon preparation that is necessary for standard colonoscopy.

Instead of a colonoscopy, a patient may have a flexible sigmoidoscopy. Similar to a colonoscopy, this procedure uses a shorter tube to investigate the lower parts of the colon (sigmoid colon and descending colon). Sigmoidoscopies produce less discomfort than colonoscopies, but they check only part of the colon rather than the entire colon. Patients should weigh the relative advantages and disadvantages of each type of procedure and consult with a physician about which test is best for them.

There are other tests that are also used to screen the rectum and colon for abnormalities. These include:

• Stool blood tests. The primary version of this test is known as a fecal occult blood test (FOBT). The patient is provided a kit that allows them to collect a stool sample at home. The sample is then analyzed for traces of hidden blood. If blood is found, further testing may be required. A newer stool blood test called a fecal immunochemical test (FIT) may be easier for some to use and may produce fewer false positives.
  
  
• Barium enema. A chalky substance called barium is inserted to fill and distend the colon. Air is then pumped in to expand the colon, and x-rays are taken. This procedure is not as accurate as a colonoscopy, and is generally used only when a patient cannot undergo a colonoscopy or does not have access to the procedure.

A newer version of the colonoscopy called a virtual colonoscopy creates detailed two- and three-dimensional x-ray images of the colon without using a conventional colonoscope. It can be performed using a computed axial tomography (CAT) scan, which uses special x-ray equipment to obtain cross-sectional pictures of the body; or magnetic resonance imaging (MRI), which uses a large magnet, radio waves and a computer to produce images rather than x-rays.

Proper preparation is critical to the success of the colonoscopy. Patients are urged to inform their physician about any medications they are taking, including aspirin, arthritis medications, anticoagulants (drugs that prevent the blood from clotting), diabetes medications and vitamins that contain iron. They should disclose information about any allergies they may have to drugs or other substances. They should also inform their physician of medical conditions that may require special attention, such as heart disease or lung disease.

Patients must take steps to ensure their colon is clear of stool and fluids that can obscure the view of the colon’s interior lining. Although this can be uncomfortable, it is essential that the colon be clean for the colonoscopy to provide adequate information. The physician will give the patient detailed instructions on how to prepare for the test.

During the 24 hours prior to the exam, patients are likely to be asked to:

• Stop taking iron pills or medications containing iron. Iron alters the color of the colon lining. It is likely that patients will be asked to give up these sources of iron for several days before the test. Patients may be instructed to stop taking other over–the–counter and prescription medications as well. The patient’s physician will provide specific instructions regarding mediation restrictions.
  
  Patients who have diabetes or who take anticoagulants (including aspirin) may have to prepare for the test in a slightly different manner. This should be discussed with a physician at least a week before the scheduled date of the colonoscopy.
  
  
• Take laxatives. Most patients will take a laxative the night before the exam and possibly the morning of the exam. The physician will instruct the patient on the type of laxative to use and the schedule. In some cases, a patient may also need an enema (which involves inserting fluid into the rectum) to clear the colon. In addition, the U.S. Food and Drug Administration recently approved the use of sodium phosphate in tablet form for bowel cleansing in individuals who are unable to tolerate liquid preparations. The cleansing process will vary by patient and will be prescribed by the physician performing the procedure.
  
  Patients will likely spend a significant amount of time in the bathroom in the 24 hours prior to testing. Although patients may find this unpleasant, it is crucial to   clean out the colon so the physician can get a detailed look at the colon wall.
  
  
• Avoid eating solid foods and opaque liquids until after the procedure. Some physicians may recommend that patients avoid these for one to three days prior to the test.
  
  
• Drink and eat only clear, nonalcoholic beverages and foods. These might include water, tea, gelatin that is not red (as red can be mistaken for blood), clear broth and certain juices. Patients must avoid all red liquids. The physician will instruct the patient on specific dietary guidelines and restrictions prior to the colonoscopy.

The day of the test, the patient is restricted to drinking clear, nonalcoholic liquids up to two to four hours before the exam. After that point, the patient may not consume any liquids or take any medications until the procedure is finished.

The colonoscopy may take place in a hospital or in an outpatient office. The procedure is performed by a gastroenterologist, a physician with expertise in gastrointestinal disorders.

Although a properly performed colonoscopy produces little discomfort, patients are given sedatives that sometimes may be combined with pain medication. The patient will have an intravenous (I.V.) line placed for delivery of these drugs. The medications will cause the patient to be either fully asleep or very drowsy and comfortable throughout the procedure. Many patients find that the sedative will prevent them from remembering much of the test.

During the procedure, patients lie on their left side on a table. The physician will lubricate a gloved finger and perform a digital rectal exam. A long colonoscope is then lubricated and inserted into the rectum. This tube – which is about the width of a finger – has a fiber–optic light and a tiny video camera on its tip that the physician uses to search for abnormalities. If awake, the patient may feel a desire to have a bowel movement. This is normal and should not cause concern.

The physician can also send air into the tube channel that inflates the colon, providing a clearer view of its interior lining. As this air enters the colon, the patient may feel cramping or a sense of fullness. However, this discomfort is likely to be minor. Patients can reduce the discomfort by taking slow, deep breaths.

The colonoscope is gently inserted further into the colon until the physician can see the entire colon. The camera at the end of the colonoscope captures images that are transmitted to an external monitor. If an abnormality is discovered, the physician can insert an instrument into the colonoscope channel and perform one of several options:

• Remove the growth
  
  
• Take a biopsy of the abnormal tissue to be sent to a laboratory for analysis
  
  
• Inject solutions or cauterize (destroy) the abnormal tissue

If bleeding occurs during removal of a polyp or other tissue, a laser, heater probe, electrical probe or special medicine can be delivered through the colonoscope to stop the bleeding. In some cases, the physician may decide to wait and remove an abnormality during a separate procedure.

A colonoscopy exam typically takes between 15 minutes and an hour, and research suggests that physicians who spend at least six minutes looking for abnormalities during an initial screening tend to have better results.

In the first hour after the procedure, the patient will begin to slowly recover from the sedative. The physician will be able to provide the patient with initial results of the colonoscopy. However, the final results of the test, including any biopsies, will take additional time. These results may be discussed with the patient during a follow–up visit.

Patients should have someone drive them home after the procedure as the full effects of the sedative may not wear off for 24 hours. Patients should spend the remainder of the day relaxing. The physician will inform the patient of when it is safe to eat and drink again, as well as when a normal routine can be resumed. Some patients who use anticoagulants (drugs that prevent the blood from clotting) may be asked to suspend their medication routine for a period of time, especially if a biopsy sample was taken or a polyp was removed.

It is normal to feel bloated or to have gas for a few hours following the exam. Taking a pain reliever or walking may help relieve the discomfort. Some patients may experience nausea from the sedation. Patients may have small amounts of blood in their first bowel movement if a biopsy was performed during the procedure. This is normal and should not cause concern. Symptoms that may indicate a problem and the need to contact a physician include:

• Persistent nausea
• Persistent but minor bleeding
• Ongoing bloating or pain in the abdomen

Some symptoms following a colonoscopy indicate the need for immediate medical attention. These symptoms include:

• Severe pain or cramping in the abdomen
• Heavy bleeding from the rectum
• Fever
• Vomiting
• Dizziness
• Weakness

Before each procedure, the colonoscope is sterilized, which virtually eliminates the risk of infection. Some patients may feel some abdominal cramping or pressure when the physician pumps air into the colon to inflate it for better viewing.

Patients may have some blood in their first bowel movement after the procedure. This is normal. However, continued blood in the stool, abdominal pain or a fever of 100 degrees Fahrenheit (38 degrees Celsius) may indicate perforation of the colon or rectal wall. Although this is rare, it may require surgical repair to prevent significant bleeding. The risk of such perforation is higher in patients who have had a polyp removed during the colonoscopy.

In some cases, removal of a polyp or tissue sample for biopsy can cause heavy bleeding (hemorrhage) that may require a blood transfusion.

There is also the risk that some abnormalities may go undetected in a coloscopy. This may be affected by poor bowel preparation before the procedure, the skill of the physician in using the colonoscope and the patient’s anatomy.

Some research suggests that the risks of colonoscopies outweigh the potential benefits in individuals age 80 and older. All patients should address any concerns they may have about colonoscopies with their physician.

In many cases, abnormalities discovered during a colonoscopy will be removed immediately. However, in some cases, a separate follow-up procedure will be scheduled to eliminate the problem. In addition, some colonoscopies do not present a full picture of the patient’s colon because areas of the colon may have been visually obscured by the presence of stool or another factor. In such cases, a physician may recommend a follow-up within a year.

Patients who have no abnormalities will probably not require another colonoscopy for several years. However, at some point in the future the patient will have to have the procedure repeated to make sure new growths have not formed. A patient’s physician is best qualified to determine an appropriate colonoscopy schedule.  The American College of Gastroenterology makes the following recommendations:

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following colonoscopy-related questions:

1. Why is a colonoscopy the most appropriate test for me?
   
   
2. Are there any other tests I can take in place of a colonoscopy?
   
   
3. What condition do you suspect I may have? Which other types of abnormalities can be detected through a colonoscopy?
   
   
4. Will I need to go on a liquid diet to prepare for my colonoscopy?
   
   
5. How will the test results be affected if I forget to comply with your preparatory suggestions?
   
   
6. Do I have to alter the way I take my daily medications in anticipation of the colonoscopy?
   
   
7. Will the procedure be uncomfortable? How can I reduce this discomfort?
   
   
8. How long will my colonoscopy take?
   
   
9. Will I need someone to drive me home after the colonoscopy?
   
   
10. I had a colonoscopy last week, and now I’m experiencing heavy blood in my stool. Should I be concerned?
    
    
11. At what age should I start scheduling routine colonoscopies?
    
    
12. Should my relatives schedule a colonoscopy?