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What is a colonoscopy?

A colonoscopy is a procedure that examines the lining of your colon and rectum using a thin, flexible instrument called a colonoscope. The colonoscope has a camera that transmits pictures of the inside of your colon to a video screen.

The colon and the rectum make up the large intestine, sometimes called the large bowel. The large intestine is a long, hollow organ in your abdomen that plays an important role in digestion by removing water from digested material and forming feces.  

A colonoscopy is an important test that can detect colorectal cancer in its earliest, most curable stage. It also helps diagnose unexplained intestinal symptoms, such as changes in your bowel movements, abdominal pain, or rectal bleeding

Colonoscopy is only one method used to test for colon cancer. Discuss all the screening and testing options with your doctor to understand which options are right for you.

Types of colonoscopy

The types of colonoscopy procedures include:

  • Colonoscopy is an endoscopy procedure that involves inserting a colonoscope into the large intestine through the anus. The colonoscope contains a camera that transmits pictures of the inside of your colon to a video screen.

  • Virtual colonoscopy is a type of computerized tomography (CT) scan that uses X-rays to produce images of the inside of the large intestine. Despite its name, virtual colonoscopy is not an actual endoscopy procedure because it does not involve inserting a colonoscope into the large intestine.

Other procedures that may be performed

Your doctor may perform other procedures in addition to colonoscopy to diagnose or treat certain conditions. These include:

  • Control of bleeding in the large intestine. This involves injecting medications, applying clips, or sealing bleeding vessels with heat

  • Removal of colon polyps, which are abnormal growths in the large intestine that can become cancerous

  • Tissue biopsy, which involves removing polyps or samples of abnormal looking intestinal tissues. Tissues are examined and tested in a lab for cancer and other diseases.

Why is a colonoscopy performed? 

Your doctor may recommend a colonoscopy to diagnose and treat diseases and conditions of the colon and rectum including:

  • Abdominal pain if the underlying cause has not been found through less invasive testing. Abdominal pain can be caused by many different conditions, such as inflammatory bowel disease, diverticulitis, and intestinal ulcer.

  • Anemia (low red blood cell count) if the underlying cause has not been found through less invasive testing. A colonoscopy can be used to identify potential bleeding sites.

  • Bleeding symptoms, such as rectal bleeding, bloody stool, or black, tarry feces. Potential causes include colon cancer and intestinal inflammation or damage.

  • Bowel movement changes, such as pencil thin stools. Bowel movement changes are caused by various conditions, such as intestinal inflammation and colon cancer.

  • Colon polyps, abnormal growths in the large intestine that can become cancerous. In some cases, polyps are first identified during another procedure called a barium enema and removed during colonoscopy.

  • Colorectal cancer screening. A colonoscopy can identify and remove abnormal tissue and colon polyps before they develop into cancer.

  • Diarrhea. A colonoscopy can identify inflammation and infections.

  • Diverticulosis and diverticulitis, intestinal pockets that can develop over time and can become infected or cause bleeding

  • Inflammatory bowel disease, which includes ulcerative colitis and Crohn's disease

  • Unexplained weight loss if the underlying cause has not been found through other, less invasive tests

Who performs a colonoscopy?

The following doctors commonly perform colonoscopies:

  • Gastroenterologists are internists who specialize in diseases of the intestines. Gastroenterologists perform most colonoscopies.

Other doctors who perform colonoscopies: 

  • Colon and rectal surgeons are general surgeons with extra training in the surgical treatment of intestinal and rectal conditions.

  • General surgeons specialize in the surgical treatment of a variety of diseases, disorders and conditions. Some general surgeons focus their practice on the intestinal tract.

How is a colonoscopy performed?

Your colonoscopy will be performed in a hospital or outpatient setting. The procedure takes about 30 minutes and generally includes these steps:

  1. You will dress in a patient gown.

  2. You will lie on your left side on a procedure table and pull your knees up to your chest.

  3. You will have a light sedative to make you drowsy and relaxed and a pain medication. Deeper sedation or anesthesia is sometimes used, which makes you more relaxed and unaware of the procedure.

  4. Your doctor will gently insert the colonoscope through the anus and into the rectum and colon. The image is transmitted onto a video screen.

  5. Your doctor will insert air into the colon. Stool and fluids are removed through the colonoscope as needed. This improves the view of the intestinal lining.

  6. Your doctor will slowly and gently pull the colonoscope out of the colon and rectum, examining it for any abnormalities. This is when the most careful examination is carried out and images are taken. Other procedures may be performed during this time, such as a tissue biopsy.

Will I feel pain?

Your comfort and relaxation are important to you and your care team. You may feel pressure and brief cramping during the procedure. Your doctor will give you enough pain and sedative medications so you stay comfortable. Tell your doctor if you are uncomfortable in any way.

What are the risks and potential complications of a colonoscopy?  

Complications of a colonoscopy are uncommon, but any procedure involves risks and the possibility of complications that may become serious in some cases. Complications can develop during the procedure or recovery. Risks and potential complications of a colonoscopy include: 

  • Adverse reaction or problems related to sedation or medications, such as an allergic reaction and problems with breathing

  • Bleeding

  • Dehydration due to taking enemas and laxatives before the procedure

  • Gastrointestinal disturbances, such as nausea, vomiting, and rectal discomfort

  • Infection

  • Puncture of the large intestine

Reducing your risk of complications

You can reduce the risk of certain complications by: 

  • Following activity, dietary and lifestyle restrictions and recommendations before your procedure and during recovery

  • Notifying your doctor immediately of any concerns, such as bleeding, fever, or increase in pain

  • Taking your medications exactly as directed

  • Telling all members of your care team if you have any allergies

How do I prepare for my colonoscopy?

You are an important member of your own healthcare team. The steps you take before your colonoscopy can improve your comfort and help get the most accurate test results. 

You can prepare for a colonoscopy by:

  • Answering all questions about your medical history and medications. This includes prescriptions, over-the-counter drugs, herbal treatments, and vitamins. It is a good idea to carry a current list of your medical conditions, medications, and allergies at all times.

  • Completely cleansing your intestines as directed by your doctor. This may include a combination of enemas, laxatives, and not eating solid foods for a day.

  • Drinking plenty of clear fluids to be well hydrated 

  • Taking or stopping medications exactly as directed. This may include not taking aspirin, ibuprofen (Advil, Motrin), and blood thinners. Your doctor will give you individualized instructions for taking your specific medications and supplements.

Questions to ask your doctor

Preparing for a colonoscopy can be stressful. It is common for patients to forget some of their questions during a brief doctor’s office visit. You may also think of other questions after your appointment.  Contact your doctor with concerns and questions before a colonoscopy and between appointments. 

It is also a good idea to bring a list of questions to your appointment. Questions can include:

  • Why do I need a colonoscopy? Are there any other options for diagnosing or treating my condition?

  • How long will the procedure take? When can I go home?

  • What restrictions will I have after the procedure? When can I return to work and other activities?

  • What kind of assistance will I need at home? Will I need a ride home?

  • How should I take my medications? 

  • How will you treat my pain?

  • When will I receive the results of my test?

  • When should I follow up with you?

  • When and how should I contact you? Ask for numbers to call during and after regular hours.

What can I expect after my colonoscopy?

Knowing what to expect after a colonoscopy can help you get back to your everyday life as soon as possible.

How will I feel after the colonoscopy?

You might feel drowsy from the sedative and pain medications. You may have mild temporary abdominal cramping and pass the gas that was inserted during the procedure. To reduce discomfort, take slow deep breaths to relax your abdominal muscles. Your doctor will treat your pain as needed. Tell your doctor if your pain is not well controlled by medication.

When can I go home?

You will be discharged home when you are alert, breathing effectively, and your vital signs are stable. This generally takes less than an hour, depending on the type of sedation you have. 

You cannot drive for about 24 hours and will need a ride home because you may still be drowsy. It is a good idea for someone to stay with you for the first day or so.

When should I call my doctor?

It is important to keep your follow-up appointments after a colonoscopy. Contact your doctor for questions and concerns between appointments. Call your doctor or seek immediate medical care if you have:

  • Bleeding

  • Fever (you should not have any fever after a minor testing procedure)

  • Pain that is not controlled by your pain medication

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Nov 14
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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  2. Evaluating postoperative fever: A focused approach. Cleveland Clinic Journal of Medicine.
  3. Frequently Asked Questions About Colonoscopy and Sigmoidoscopy. American Cancer Society.
  4. Learn About Cancer. American Cancer Society.
  5. Understanding Colonoscopy. American Society for Gastrointestinal Endoscopy.