What Is a Colonoscopy?

<p>John Fedele / Getty Images</p>

John Fedele / Getty Images

Medically reviewed by Robert Burakoff, MD

A colonoscopy is a common procedure for examining the bowel, also called the colon or intestine. A gastroenterologist (a doctor specializing in the digestive system) inserts a flexible tube through the rectum and into the large colon.

Another type of colonoscopy is called a virtual colonoscopy. Technologists or other medical staff use CT (computer tomography) scans to produce an image the bowel from outside the body.

Gastroenterologists use colonoscopies to look for signs of disease, polyps, growths, or cancer. They can also use the procedure to perform biopsies (removal of cells or tissue for examination).

  • There are two types of colonoscopy. An optical colonoscopy involves inserting a flexible tube into the rectum and colon while a virtual colonoscopy views the colon with x-rays.

  • Colonoscopy screens for signs of colorectal cancer or irritable bowel diseases like Crohn's or ulcerative colitis.

  • Risks of colonoscopy include bleeding, adverse reaction to anesthetics, and in some cases, bowel perforation.

  • If the gastroenterologist finds any abnormalities inside the colon or rectum, the test will come back positive. A biopsy can help determine whether growths are cancerous.


A gastroenterologist will perform a colonoscopy to find the cause of symptoms including anal bleeding, changes in bowel activity, abdominal pain, and unexplained weight loss.

A colonoscopy is also a screening tool for colon polyps and cancer recommended for people over the age of 45. It is the only tool capable of finding, confirming, and removing polyps.

The test results could lead to the accurate diagnosis of multiple conditions including:

  • Colorectal cancer. A form of cancer that grows out of the intestinal lining in the rectum or colon.

  • Polyps. Abnormal tissue that grows out of the intestinal lining. These are usually non-cancerous, but may turn into cancer.

  • Ulcers. A hole within the lining of the large intestine.

  • Irritated or swollen tissue. A sign of disease or infection.

  • Crohn's disease. An inflammatory bowel disease that causes chronic inflammation throughout the large intestine.

  • Ulcerative colitis. An inflammatory bowel disease that causes chronic inflammation and ulcers within the lining of the large intestine.

Types of Colonoscopy

There are two different types of colonoscopy. Depending on your reason for the procedure, health risks, and comfort level, your healthcare provider may recommend one over the other.

Optical Colonoscopy

An optical colonoscopy involves the insertion of a thin, flexible tube into the anus and rectum. The tube, called a colonoscope, has a light and a lens on the end for viewing the colon. Optical colonoscopy is recommended for patients with a high risk of colorectal cancer.

Optical colonoscopy is better at finding small growths and polyps than virtual colonoscopy. The healthcare provider is also able perform a biopsy during the procedure if they detect an abnormal growth.

This procedure requires anesthesia or sedatives and takes 30 to 60 minutes.

Virtual Colonoscopy

A virtual colonoscopy uses CT scans (an imaging technique using x-rays) to see the entire colon from the outside. This procedure does not require anesthesia. It's also less invasive and takes less time than an optical colonoscopy—about 10 to 15 minutes. However, it may miss smaller polyps.

If a virtual colonoscopy does show any abnormalities, your healthcare provider will recommend an optical colonoscopy to confirm the results.

How Does It Work

A gastroenterologist will perform your colonoscopy at a hospital or outpatient clinic. Typically, other technicians and medical staff will be there to assist with the procedure. Your healthcare provider can give more information about your specific procedure as well as preparation instructions.

Before the Test

For an optical colonoscopy, you will be laid onto a table on your left side or back. Medical staff will insert an intravenous (IV) needle into your arm or hand to deliver anesthesia or sedatives. This makes the procedure painless.

Before a virtual colonoscopy, you will drink contrast medium, a type of ingestible dye that shows up on x-rays to help make polyps more visible.

For both types of colonoscopy, the medical staff will check your blood pressure, oxygen levels, and pulse prior to the start of the procedure.

During the Test

In an optical colonoscopy, a gastroenterologist will insert a flexible tube with a small camera into the rectum and colon. The tube may pump air into the large intestine to inflate it, making it easier to view the intestinal lining.

The gastroenterologist will be able to view the colon on a screen showing live video feed from the camera. Once the tube has reached the end of the large intestine, the gastroenterologist will retract it slowly, looking over the colon again.

If there are any growths, polyps, or abnormal tissue in the colon, the gastroenterologist will remove them for testing. If there is a source of bleeding, the gastroenterologist may inject a medication or cauterize (apply heat) to the site to control the bleeding. Due to anesthetics, will not be aware during the procedure or feel any pain.

In a virtual colonoscopy, medical staff will insert a small tube inside the rectum to fill the colon with air to make the images clearer. Then you will be asked to lie on your back as medical staff move the examination table into a CT machine for scanning.

After the first scan is complete, you will need to turn onto your stomach or side for another scan. You will be awake for this procedure and able to communicate with the provider. While you may feel some discomfort from the air, the procedure should not be painful.

After the Test

After an optical colonoscopy, medical staff will monitor you for one to two hours while the anesthetics wear off. You may feel cramping in the abdomen for a short time following the procedure. Afterward, you will be sent home with your pre-arranged ride. A caretaker or family member may receive instructions to care for you until full recovery.

After a virtual colonoscopy, you may feel temporary bloating or abdominal cramping. You can resume regular activities immediately.

Risks and Precautions

Colonoscopies are a safe, life-saving procedure. Research shows there are only about three to 15 serious complications for every 10,000 colonoscopies.

There is some risk that inflating the colon with air may cause tears in the colon's lining. This must be treated immediately with surgery.

There are additional risks for optical colonoscopy including:

  • Bleeding, abdominal pain, or bloating. Bleeding may occur from polyp removal and can be treated during the procedure. You may experience bleeding for two weeks following the procedure, along with pain and bloating.

  • Adverse reaction to anesthesia or sedative, including stroke, heart attack, respiratory distress, and potentially death.

  • Intestinal perforation. Perforation, or puncture, of the colon is estimated to occur in about 1 in 1,000 colonoscopies. This can happen as a result of removing polyps, putting pressure against the colon wall, or blowing too much air into a weakened colon.

A virtual colonoscopy delivers a small dose of radiation, which may cause an increased risk of cancer. However, more research is needed to determine whether the benefits outweigh this risk.

When to Seek Immediate Help

If any of these symptoms persist after a colonoscopy, they are cause for concern. Seek immediate medical care if you experience:

  • Severe abdominal pain

  • Bloody bowel movements or anal bleeding that does not stop

  • Dizziness or weakness

  • Fever

How To Prepare for a Colonoscopy

Before a colonoscopy, speak with your gastroenterologist about any health conditions, medications, and supplements you take regularly. You will need to temporarily adjust your diet and arrange for a ride home afterward.

Make a Plan for Medications

While most medications can be taken as usual before colonoscopy, some interfere with bowel preparation and safety. Talk to your healthcare provider about any medications you are taking before the procedure. If you need to stop any medications, ask them for how long.

Medications that may interfere with a colonoscopy procedure include:

  • Insulin or diabetes medication, including Sexenda (liraglutide), Byetta (exenatide), Trulicity (dulaglutide).

  • Aspirin.

  • Arthritis medications, including Aleve (naproxen), Celebrex (celecoxib), Motrin (ibuprofen).

  • Blood thinners, including Coumadin (warfarin), Eliquis (apixaban), Xarelto (rivaroxaban), Lovenox (heparin).

  • Anti-clotting medications, including Plavix (clopidogrel), Brilinta (ticagrelor), Effient (prasugrel).

  • Over-the-counter medications and supplements. These should not be taken the morning of the procedure.

You should also let your healthcare provider or gastroenterologist know if you have any allergies to medications, especially anesthetics.

Follow Fasting and Bowel Cleansing Instructions

It's important to follow instructions to prepare your bowel before the colonoscopy. There needs to be little or no stool remaining in the intestines in order to examine the colon lining. If the bowel is not clear enough, the gastroenterologist may need to postpone the colonoscopy.

Prior to the colonoscopy, you may need to consume a clear liquid diet for one to three days leading up to the procedure. While on the clear liquid diet, you can eat or drink:

  • Water

  • Plain tea or coffee without cream or milk

  • Fat-free bouillon or broth

  • Some flavors of gelatin

  • Some types of sports drinks

  • Apple juice or white grape juice

Many bowel preps involve taking laxatives. These are pills or powders that soften the stool, making it easier to pass. In some cases, the patient may need to drink a large amount of liquid laxatives the night before and morning of the procedure.

Additionally, the gastroenterologist may prescribe an enema, which is an injection of fluids into the rectum to cleanse the colon or cause a bowel movement. The bowel prep will cause diarrhea so it is important to stay near a bathroom.

Arrange a Ride Home

In the case of an optical colonoscopy, you will receive anesthesia or sedatives during the procedure. You will not be able to drive for 24 hours afterward. Make sure to ask a friend or family member ahead of time to give you a ride home after the procedure.

Wear Comfortable Clothing

You will need to change into a gown for the procedure, but it's best to wear comfortable clothes for any tests before and for going home afterwards. If you are having a virtual colonoscopy, make sure to not bring any personal electronics into the imaging room as the CT machine may damage them.

Check Your Insurance Coverage

The Affordable Care Act requires private insurers and Medicare to cover the costs of colorectal cancer screening tests, like colonoscopy. However, it's still a good idea to check with your insurance company to understand the cost of the procedure.


If the gastroenterologist finds polyps or abnormal tissue during an optical colonoscopy, they will cut it out and perform laboratory tests on it. If there are abnormalities in a virtual colonoscopy, you may need to undergo an optical colonoscopy.

Interpreting Your Results

The gastroenterologist will tell you about any abnormalities in your colon right after the procedure. If they cut out tissue for a biopsy, it may take several days to determine whether it is cancerous. Colonoscopy results can show as:

  • Positive. This indicates a polyp, growth, or other abnormality was found in the large intestine. In most cases, polyps are non-cancerous. Still, a biopsy of the tissue will be sent to a lab to determine if it's potentially cancerous or shows other signs of disease.

  • Inconclusive. In up to 25% of cases, the results are inconclusive. This means an incomplete bowel prep or other factors prevented the gastroenterologist from completing the procedure.

  • Negative. This indicates the gastroenterologist did not detect any polyps or other abnormalities during the colonoscopy.

After a positive test, the gastroenterologist may suggest more frequent testing. This recommendation may be based on the amount and size of polyps or growths found, and whether any of the polyps were potentially cancerous.

A Quick Review

Colonoscopy is a procedure used to screen and diagnose the early signs of colorectal cancer and other bowel diseases. The most common type of colonoscopy involves inserting a flexible tube with a camera into the bowel to examine the intestinal lining for abnormal growths.

Prior to a colonoscopy, you will need to follow a clear liquid diet in order to cleanse your bowel. You should also talk to your gastroenterologist about any medications you are taking as some might interfere with the procedure.

Colonoscopies are relatively safe. You may experience some abdominal discomfort or bleeding after the procedure. Seek medical help if you have severe pain, bloody stools, or fever after the colonoscopy.

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