Colonoscopy: Uses, Side Effects, Procedure, and Results

In This Article

A colonoscopy is a procedure that may be done to screen for colon cancer if there is a reason to suspect it. The test has significantly reduced the risk of dying from the disease. After a person is sedated, a flexible, lighted tube equipped with a tiny TV camera, called a colonoscope, is inserted into the rectum and threaded through the colon to look for any evidence of cancer, polyps, ulcers, and more.

If any abnormalities are noted, a biopsy or polyp removal may be done to aid in the diagnosis of colon cancer, precancerous polyps, or other concerns, like inflammatory bowel disease.

what to expect during a colonoscopy
 Illustration by Cindy Chung, Verywell

Purpose of Test

A colonoscopy may be done as a screening test (screening colonoscopy) to look for any evidence of cancer or polyps, or as a diagnostic test (diagnostic colonoscopy) when certain issues are suspected.


While there has been controversy over the benefit of some cancer screening tests, such as PSA tests for prostate cancer, screening colonoscopy has clearly been shown to reduce the risk that a person will die from colon cancer.

Colonoscopy is also somewhat unique among cancer screening tests. Most screening tests are done in an attempt to find cancer in the earliest of stages, something referred to as "early detection." Yet a colonoscopy may also play a role in prevention. If a precancerous polyp is found and removed before it has time to develop into a cancerous tumor, a colonoscopy may also prevent colon cancer from occurring in the first place.

For those at average risk of developing colon cancer, some medical organizations recommend a screening colonoscopy at age 50 and every 10 years thereafter if results are initially normal. Alternatively, the American Cancer Society recommends screening starting at age 45 for those at average risk. Screening is also recommended at a younger age (and more often) for those who have risk factors for colon cancer, such as:

  • A family history of the disease
  • Hereditary syndromes, such as Lynch syndrome or familial adenomatous polyposis
  • A history of precancerous polyps
  • A history of inflammatory bowel disease (IBS), such as Crohn's disease or ulcerative colitis. With IBS, a colonoscopy will sometimes need to be done as regularly as every year to evaluate the level of inflammation and effect the disease is having on the colon.


A diagnostic colonoscopy may be recommended for those who have symptoms or signs of colon cancer, such as:

Masses or changes in the bowel may signal the presence of cancer, and a biopsy is usually needed to confirm or refute the diagnosis.

Colonoscopy can also detect:

  • Colon polyps: Both precancerous and non-precancerous types
  • Source of rectal bleeding, if present
  • Ulcers
  • Fistulas: Abnormal passageways between the colon and other regions of the body, such as the skin around the rectum, may occur with conditions such as Crohn's disease.

Complementary Tests

If an abnormal region or mass in the colon is found during a colonoscopy, a special attachment at the end of the colonoscope may be used to take a biopsy. If a polyp is found, it may be removed using a wire loop attachment on the colonoscope (polypectomy). Samples are sent to a laboratory for further testing.


For roughly 10 percent of people, the colonoscope cannot be inserted all the way to the beginning of the colon (right colon). A significant number of colon cancers are found in this area. These individuals may need a repeat colonoscopy or a virtual colonoscopy to evaluate this region.

Similar Tests

Unlike a conventional colonoscopy, which is invasive, a virtual colonoscopy (also called CT colonography) involves indirect observation of the colon via a CT scan after a person drinks a contrast solution. Virtual colonoscopy is recommended every five years, compared with 10 years for a conventional procedure.

For people at average risk of developing colon cancer, the procedures offer similar efficacy, though a virtual colonoscopy is less likely to detect flat lesions (sessile lesions) or small (less than 6 millimeters) polyps. For those who have an elevated risk of colon cancer, have symptoms such as bleeding, or have inflammatory bowel disease, conventional colonoscopy is the preferred approach.

One of the clear advantages of a conventional colonoscopy is that a biopsy or polyp removal can be done during the procedure. If any of these lesions are detected on a virtual colonoscopy, a conventional colonoscopy will then need to be done (and the colon preparation may need to be repeated unless the tests can be done the same day).

Other Tests

Other tests have been evaluated over the years in an attempt to detect colon cancer in the earliest of stages, though none are as effective as colonoscopy. A guaiac smear test (combined with a physician's rectal exam) or a fecal occult blood test (tests done on three separate bowel movements at home) may detect blood, and, according to the National Cancer Institute, the guaiac smear is a useful screening test when done every one to two years.

Barium enemas have also been evaluated, but miss significantly more cancers than a colonoscopy. In this procedure, an X-ray study is done after barium is inserted into the colon.

Flexible sigmoidoscopy is another screening option, but its use has declined due to the greater efficacy of colonoscopy. A sigmoidoscopy uses a tube to screen for colon cancer or polyps similar to a colonoscopy, but only evaluates the left side of the colon. As such, sigmoidoscopy misses a substantial number of colon cancers and polyps.

Risks and Contraindications

Like any medical procedure, a colonoscopy carries potential risks (some related to test preparation, some related to the procedure itself), as well as reasons the test should not be performed.

Preparation Risks

In order to have a colonoscopy, all fecal matter must be removed from the colon. Your doctor will advise you as to the steps to take to do this (further details below).

Fluid overload (due to the large volume of fluid ingested with some laxatives) and electrolyte imbalances (due to enema use) may occur as a result of this effort, but this is primarily a concern for those who have medical conditions such as congestive heart failure or kidney disease.

Procedure Risks

Potential risks of a colonoscopy procedure itself include:

  • Bleeding—Bleeding occurs in roughly 1 of 1,000 colonoscopies and is more likely to occur when a polyp is removed. Most of the time, bleeding resolves on its own without any treatment.
  • Infection—Infections are uncommon after a colonoscopy, but are more likely to occur with inadequate colon preparation.
  • Colon perforation—Perforation of the colon (a tear in the colon) may occur either when the air is injected into the colon or if an instrument perforates the bowel. A 2013 study looking at over 80,000 colonoscopies published in the World Journal of Gastroenterology found that the rate of perforation was 0.06 percent. Risk factors included increased age, being hospitalized (in intensive care) at the time of the procedure, a history of abdominal pain, and Crohn's disease. In this study, those who had a biopsy or polyp removal did not have an increased risk of perforation.
  • Postpolypectomy syndrome—Postpolypectomy syndrome occurs in roughly 1 in 1,000 colonoscopies, and is most common when a polyp is removed and electrocoagulation (cautery or burning) is used to stop the bleeding at the base of the polyp. Symptoms include fever, abdominal pain, and an elevated white blood cell count.
  • Risk of a reaction or allergy to the anesthetic used for sedation


There are no absolute contraindications for a colonoscopy, but there are particular times when the potential benefits of the procedure should be weighed against the risks, including cases of fulminant colitis with ulcerations of the colon (this could increase the risk of perforation) and toxic megacolon.

Colonoscopy should only be done if absolutely necessary during pregnancy (such as if colon cancer is suspected or if a colonoscopy could be used instead of colon surgery).

Before the Test

When you set up your procedure, your doctor will talk to you about the benefits and potential risks of colonoscopy, any symptoms you are having, and any risk factors you have for colon cancer. If you have had a colonoscopy or other colon cancer screening procedure in the past, your doctor will ask you to obtain your records if the tests were done at a different clinic or hospital. She will also talk to you about the importance of having a regular colonoscopy and try to reduce any fears or concerns you have about the procedure. If you have questions, be sure to ask them.


The average time required for the colonoscopy procedure itself is around 30 minutes, but it's important to consider the big picture when planning for this test, as it will require preparation steps that may need to start several days before the procedure, as well as recovery time.

When you arrive on the day of your test, you will need time for a nurse to place an IV and talk about the procedure and anesthesia. After the procedure, people can take variable amounts of time until they are fully alert and ready to leave.


A colonoscopy may be done at an outpatient endoscopy center or at a hospital. These locations are equipped to monitor you while you receive anesthesia and are prepared to handle any emergencies that could arise.

Colon Preparation

The preparation for a colonoscopy to clear the bowel of all fecal matter is often considered the most challenging part of the procedure. While the preparation can take some time and may even feel like overkill, it's important to follow each step carefully. It's not uncommon for colonoscopies to be rescheduled due to an inadequate colon preparation, as this can affect results. Unfortunately, that means that the preparation needs to be done all over again.

Most of the time, a combination of laxatives and enemas are used to clean the colon. Laxatives work by stimulating passage of stool from the colon (by causing diarrhea) and may be used in either pill or liquid form. Some of these preparations require that you drink up to a gallon of water, and those who have a history of heart failure or kidney disease should talk to their doctor about the best approach. For those who are elderly or have medical conditions such as kidney disease, preparations with polyethylene glycol may be safer than those containing sodium phosphate solutions.

Enemas involve inserting a solution through your anus into your colon, holding the solution for a period of time, and then passing stool.

Plan to have easy access to a bathroom the entire day before your procedure.

Food and Drink

Starting three days (and up to a week) before your colonoscopy, you will be advised to avoid certain foods, including popcorn, seeds and nuts, raw fruits and vegetables, grains, and potato skins. These foods may stick to the folds of the colon, both interfering with adequate colon preparation and potentially getting sucked into the colonoscope during the procedure, clogging the instrument.

A day or two prior to your procedure, a clear liquid diet is usually recommended. A clear liquid diet may include water, broths, clear juices (apple juice or clear grape juice), gelatin, plain coffee (no cream), or sports drinks.

If you will be having your colonoscopy in the morning, physicians usually recommend not eating or drinking anything after midnight. If there are medications you need to take, you may be able to take these with a sip of water.


Your doctor will talk to you about what medications you may continue or need to stop before your colonoscopy. If you are on blood thinners, it is ideal to stop these prior to the procedure, but sometimes the benefits of these drugs outweigh the risks of bleeding. These medications include:

  • Anticoagulants, such as Eliquis (apixaban), Xarelto (rivaraxoban), Coumadin (warfarin), Fragmin (dalteparin), Pradaxa (dabigatran), and Lovenox (enoxaparin)
  • Anti-platelet medications, such as Plavix (clopidogrel), Effient (prasugrel), and Pletal (cilostazol)

Most physicians also recommend avoiding aspirin and nonsteroidal anti-inflammatory medications such as Advil (ibuprofen) for up to a week or two prior to the colonoscopy. Again, talk to your doctor if you are taking aspirin due to heart disease or to reduce the risk of a heart attack.

Some vitamins and dietary supplements may also increase bleeding time. Make sure to discuss not only your prescription medications but any other preparations you take with your doctor.

What to Wear

You will be changing into a gown prior to your procedure, but wearing loose, comfortable clothing, especially around your waistline, may help you feel more comfortable following the procedure. It's best to leave jewelry at home.

Cost and Health Insurance

Health insurance companies are required to cover screening colonoscopies that are ordered according to guidelines. If your doctor recommends a colonoscopy at an earlier age, or more frequently due to a medical condition, however, you may need to get a prior authorization.

The average cost of a colonoscopy is slightly greater than $3,000 and can go as high as $5,000.

There are several colonoscopy options for the uninsured or underinsured, including state programs, local programs, and assistance offered by non-profit organizations, such as the Blue Hope Financial Assistance offered by the Colon Cancer Alliance. The organization ColonoscopyAssist is a colon cancer screening program through which individuals can find a low-cost colonoscopy for $1,075.

What to Bring

You should bring any forms you have been asked to complete and your insurance card on the day of your test. It's also helpful to bring a magazine or book in case you end up waiting before the procedure. You will be asked to bring a driver (or arrange for transportation), as you will be unable to drive after the test due to the effects of the anesthesia.

During the Test

When you are brought back to the endoscopy suite, you will be attended to by a nurse and the physician performing the procedure, who will be a gastroenterologist or a colorectal surgeon.


Your nurse will review your information, confirm that you haven't eaten anything in the hours prior to the procedure, and talk about any concerns you may have. After having you remove all of your clothing and change into a gown, she will place an intravenous line in your arm, through which medications will be given to sedate you during the procedure. She will also apply electrocardiograph (EKG) recording patches to your chest to monitor your heartbeat, and place a pulse oximeter on your finger to monitor the oxygen level in your blood.

Throughout the Test

When your test begins, your nurse will help you lie on your side on a table and make sure you are comfortable. Sedative medication will then be given to help you relax. This monitored anesthesia care, also referred to as "twilight sleep," is different than general anesthesia. Though many people sleep through the procedure, you may awaken at times. That said, you will be very relaxed.

When you are adequately sedated, the doctor will insert the colonoscope into your rectum and begin threading the scope upward through your colon. To get a clearer view, some air may also be pumped through the colonoscope to open up the intestinal passage.

If any abnormal regions are noted, a biopsy will be performed via a special tool on the colonoscope. Likewise, if a polyp or polyps are found, they can be removed with a special wire loop on the scope. When the procedure is finished, the physician will remove the colonoscope.


When the procedure is finished, you will be observed in the endoscopy suite or recovery room. You may wake up shortly after the procedure or may be drowsy for some time. Because of the medications used for twilight sleep, most people don't remember the test.

When you are alert, your IV will be removed and your nurse will talk to you and the companion who drove you (if you brought one). In many cases, people are offered some food (such as crackers and juice) after waking up and before going home.

Any samples that were collected will then be sent to a pathologist for evaluation.

After the Test

You may feel drowsy for the first 24 hours and should not drive or operate machinery during this time. Due to the transient effects of anesthesia on memory, it's also recommended that people avoid making critical decisions during this time.

You should avoid strenuous activity or heavy lifting for several days after your test, but will be able to resume most ordinary daily activities, keeping the above considerations in mind. You will be able to resume your regular diet.

Managing Side Effects

Since you may experience some abdominal cramping, you will want to be near a bathroom. Often, cramping improves when you pass gas. You may also note some mild pain at the site where your IV was placed; placing warm packs on this area may help alleviate any discomfort.

When to Call Your Doctor

You should call your doctor right away if you experience moderate to heavy rectal bleeding (some slight spotting is normal, especially if a polyp was removed), feel faint or dizzy, feel short of breath, or develop chest pain or heart palpitations. You should also contact your doctor if you experience any swelling in your legs, nausea, vomiting, more-than-mild abdominal pain or cramps, fever, or chills, or you simply feel that something is not right.

In particular, abdominal pain (often severe), fever and chills, and/or nausea and vomiting may be symptoms of a perforation. While perforations may be noted immediately after or during the procedure, they may not be discovered for up to a week later. Treatment may simply involve resting the bowel but could involve endoscopic repair (repair via colonoscopy) or surgery (especially with larger perforations).

Postpolypectomy syndrome symptoms include a fever, abdominal pain, and an elevated white blood cell count, and can be easily mistaken for a perforation. Treatment includes intravenous fluids and antibiotics, though in rare cases (when the burn extends through the full thickness of the colon), delayed perforation due to the breakdown of tissue may occur.

Given the risks, it's important not to ignore these symptoms.

Interpreting Results

Some physicians will talk about your results after your procedure, whereas others will send a copy of the report to your primary care doctor, who will then share the information with you. Even if the doctor performing the test talks about your results, you should talk to your primary care doctor to confirm your understanding, as many people are groggy following the procedure.

If you haven't gotten your results within a few days, make sure to call your doctor. Don't assume that your results are normal if you do not hear anything.

Your doctor will let you know if your test was positive or negative, and if positive, what the findings were, such as the presence of ulcerations (open sores), areas of inflammation, fistulas, polyps, or cancer.

If a polyp is found and removed, or if another area is biopsied, a pathologist will be asked to look at the abnormality to determine if it is cancerous, or in the case of a polyp, what type of polyp was found and if it was precancerous or not. These results may not be available for several days.


If your colonoscopy is completely normal and you have an average risk of developing colon cancer, a follow-up test will usually be recommended in 10 years. If you have a history of polyps, you may need to be seen in five years instead. Follow-up in one year is recommended, however, if the exam was incomplete due to the presence of residual stool in the colon. For those who have other risk factors for colon cancer or colon conditions, an even earlier check may be recommended.

If your test is abnormal, follow-up will depend on the results of the test. If a precancerous polyp is found and removed, a repeat test is often recommended in five years, but should be repeated earlier if the polyp was greater than one centimeter (around half an inch) in diameter; if more than two polyps were found; or if the polyps were considered to be high risk (not all precancerous polyps are the same).

If any evidence of colon cancer is found, tests to further diagnose and stage colon cancer will be done to determine the appropriate treatment.

Other medical conditions can be found during colonoscopy as well, and follow-up and further testing will depend on the specific condition.

A Word From Verywell

It's true that having a colonoscopy is not what anyone would consider "fun." It is, however, an incredibly useful diagnostic test. Without it, more people would develop and/or die from colon cancer. In addition, people with other digestive diseases might never get an accurate diagnosis or effective treatment. A colonoscopy is definitely a test worth doing when recommended. Most people are surprised at how easy it is, and, when used for colon cancer screening, it may not need to be repeated for 10 years.

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