Colonoscopy: Purpose, Risks, Preparation, Procedure and Results

Colonoscopy is a procedure that enables a gastroenterologist to evaluate the inside of entire colon.

Updated: August 8, 2018

Colonoscopy is a procedure that enables a gastroenterologist to evaluate the inside of entire colon. The colonoscope is a four foot long, flexible tube about the thickness of a finger with a camera and a source of light at its tip. During the procedure the tip of the colonoscope is inserted into the anus and then is advanced slowly, under visual control, into the rectum and through the colon usually as far as the cecum, which is the first part of the colon.
Polyps or other types of abnormal tissue can be removed through the scope during a colonoscopy if required. Tissue samples or biopsies can be taken during a colonoscopy as well.

Purpose of Colonoscopy:

Investigate intestinal signs and symptoms:

A colonoscopy can help your doctor explore possible causes of abdominal pain, rectal bleeding, chronic constipation, chronic diarrhea and other intestinal problems.

Screen for colon cancer:

If you are age 50 or older and at average risk of colon cancer and you have no colon cancer risk factors other than age, then a colonoscopy is recommended by your doctor every 10 years or sometimes sooner to screen for colon cancer. However, how often should one undergo colonoscopy depends on the degree of the risk and the abnormalities found at previous colonoscopies. Colonoscopy is one option for colon cancer screening. Talk with your doctor about your options.

Look for more polyps:

Your doctor may recommend a follow-up colonoscopy to look for and remove any additional polyps if you have had polyps before. This is done to reduce your risk of colon cancer.

Risks of Colonoscopy:

A colonoscopy poses few risks. Rarely, complications of a colonoscopy may include:

  • Adverse reaction to the sedative used during the examination
  • Bleeding from the site where a tissue sample was taken or a polyp or other abnormal tissue was removed
  • A tear in the colon or rectum wall

Preparation for Colonoscopy:

The colon must be completely cleaned if the procedure is to be complete and accurate. Any residue in your colon may obscure the view of your colon and rectum during the examination. Patients are given detailed instructions about the cleansing preparation. These include:
Follow a special diet the day before the examination. Eating solid food is not allowed, the day before the exam. Drinks may be limited to clear liquids such as plain water, tea and coffee without milk or cream, broth, and carbonated beverages. Avoid red liquids, which can be confused with blood during the colonoscopy. You may not be able to eat or drink anything after midnight the night before the examination.
Usually taking a laxative is recommended, in either pill form or liquid form. You may be instructed to take the laxative the night before your colonoscopy, or you may be asked to use the laxative both the night before and the morning of the procedure.
Use an enema kit. In some cases, you may need to use an over the counter enema kit, either the night before the exam or a few hours before the exam to empty your colon. This is generally only effective in emptying the lower colon and is usually not recommended as a primary way of emptying your colon. As the rectum and lower intestine must be empty so that the intestinal walls can be seen, you will receive two enemas before the procedure. You will need to try to hold the enema solution for at least 5 minutes before releasing it.
Adjust your medications. Remind your doctor of your medications at least a week before the examination, especially if you have diabetes, high blood pressure or heart problems or if you take medications or supplements that contain iron.
Most medications should be continued as usual, but some may interfere with the examination. It is best to inform the colonoscopist about all current prescription and over the counter medications. Aspirin products, blood thinners such as warfarin, arthritis medications, insulin, and iron preparations are examples of medications that may require special instructions.
Let your doctor know about any special medical conditions you have. These include:

  • Pregnancy
  • Lung conditions
  • Heart conditions
  • Allergies to any medications
Other things that need to informed to your doctor include:
  • If you have diabetes or take medications that may affect blood clotting.
  • If you take aspirin or other medications that thin the blood, such as warfarin, newer anticoagulants, such as dabigatran or rivaroxaban, used to reduce risk of blot clots or stroke
  • Heart medications that affect platelets, such as clopidogrel.

You may need to adjust your dosages or stop taking the medications temporarily
Adjustments to these medications may be required before the colonoscopy. Never stop taking any medication without first consulting your doctor.
You may need to take antibiotics before the colonoscopy if you:

  • Have an artificial heart valve
  • Have ever been told you need to take antibiotics before a dental or surgical procedure

Procedure of Colonoscopy:

The colonoscopy is performed by a doctor experienced in the procedure that lasts approximately 30 to 60 minutes. Sedation is usually recommended. Sometimes a mild sedative is given in pill form or into your vein to make you feel relaxed and drowsy. You will be asked to lie on your left side on the examining table. During a colonoscopy, the doctor uses a colonoscope, which is a long, flexible, tubular instrument about half inch in diameter that transmits an image of the lining of the colon so the doctor can examine it for any abnormalities. The scope is long enough to reach the entire length of your colon. The colonoscope is inserted through the rectum and advanced to the other end of the large intestine. It contains a light and a tube that allows the doctor to pump air or carbon dioxide into your colon. The air or carbon dioxide inflates the colon, which provides a better view of the lining of the colon.
You may feel abdominal cramping or the urge to have a bowel movement when the scope is moved or air is introduced. You can reduce the cramping by taking several slow, deep breaths during the procedure. The colonoscope also contains a tiny video camera at its tip. The camera sends images to an external monitor so that the doctor can study the inside of your colon. When the doctor has finished, the colonoscope is slowly withdrawn while the lining of your bowel is carefully examined.
If the doctor sees something that may be abnormal, small amounts of tissue can be removed for analysis during the colonoscopy. Any abnormal growths, or polyps can be identified and removed during the procedure. In many cases, colonoscopy allows accurate diagnosis and treatment without the need for a major operation.

After the procedure:

Usually it takes about an hour to begin to recover from the sedative. You will need someone to take you home because it can take up to a day for the full effects of the sedative to wear off. Don't drive or make important decisions or go back to work for the rest of the day.
If your doctor removed a polyp during your colonoscopy, you may be advised to eat a special diet temporarily. You may feel bloated or pass gas for a few hours after colonoscopy as you clear the air from your colon. Walking may help relieve any discomfort. You may also notice a small amount of blood with your first bowel movement after the examination.

Certain medications, such as blood thinning agents, may need to be avoided temporarily if biopsies were taken or polyps were removed. Bleeding and puncture of the colon are rare but are possible complications of colonoscopy.
Call your doctor right away if you experience:
  • Excessive or prolonged rectal bleeding
  • Severe abdominal pain, fever, or chills

This may occur immediately or in the first few days after the procedure, but may be delayed for up to one to two weeks.


Negative result:

A colonoscopy is considered negative if the doctor doesn't find any abnormalities in the colon.
Another colonoscopy may be recommended by your doctor:

  • In 10 years, if you are at average risk of colon cancer and you have no colon cancer risk factors other than age
  • In five years, if you have a history of polyps in previous colonoscopy procedures
  • In one year, if there was residual stool in the colon that prevented complete examination of your colon

Positive result:

A colonoscopy is considered positive if the doctor finds any polyps or abnormal tissue in the colon. Most polyps aren't cancerous, but some can be precancerous. Polyps removed during colonoscopy are sent to a laboratory for analysis to determine whether they are cancerous, precancerous or noncancerous.
Depending on the size and number of polyps, you may require follow up visit to look for more polyps. A repeat colonoscopy in 5 to 10 years is recommended if your doctor finds one or two polyps less than 1 centimeter in diameter. This also depend on your other risk factors for colon cancer.
Another colonoscopy is recommended by your doctor sooner if you have:

  • More than two polyps
  • A large polyp which is larger than 1 centimeter
  • Polyps and also residual stool in the colon that prevents complete examination of the colon
  • Polyps with certain cell characteristics that indicate a higher risk of future cancer
  • Cancerous polyps

Your doctor may recommend a repeat exam with a gastroenterologist if you have a polyp or other abnormal tissue that couldn't be removed during the colonoscopy.
Gastroenterologist has special expertise in removing large polyps, or surgery.
Your doctor may recommend a repeat colonoscopy or a shorter time until your next colonoscopy if he/she is concerned about the quality of the view through the scope.
If your doctor wasn't able to advance the scope through your entire colon, a barium enema or virtual colonoscopy may be recommended to examine the rest of your colon.

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