Colonoscopy: Overview

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A colonoscopy is a procedure in which a long, flexible tube with a camera, called a colonoscope, is inserted into the rectum to look inside your colon (large intestine). Performed by a gastroenterologist, a colonoscopy is used to screen for colon cancer and to evaluate various colon-related problems like abdominal pain, rectal bleeding, or a change in bowel habits.

what to expect during a colonoscopy

Verywell / Cindy Chung

What Is a Colonoscopy?

A colonoscopy is most commonly performed as an elective procedure under mild sedation in an outpatient endoscopy center or an ambulatory surgical center. Less commonly, it is performed urgently in a hospital, often for cases of lower gastrointestinal bleeding.

After the colonoscope is inserted into the rectum, the tube is threaded through the colon so that the medical team can view it on a monitor. This allows them to look for abnormalities including polyps (tissue growths), sores (ulcers), inflammation, and bleeding.

Besides detecting tissue abnormalities, the colonoscope can be used to treat certain problems. For example, tiny instruments may be inserted through the scope to clip and remove polyps. Tissue samples, called biopsies, may also be obtained during a colonoscopy.


Absolute contraindications to a colonoscopy include:

Potential Risks

Potential risks of a colonoscopy include:

  • Bleeding: Bleeding occurs in roughly 1 of 1,000 colonoscopies and is more likely to occur when a polyp is removed.
  • Infection: Infections are rare after a colonoscopy.
  • Colon perforation: Perforation of the colon (a hole in the colon) is rare, but may occur when air is injected into the colon during the procedure to improve visualization. It can also occur if an instrument punctures the bowel. Factors that increase a person's risk for this include increased age, being hospitalized (in intensive care) at the time of the procedure, a history of abdominal pain, and Crohn's disease.
  • Postpolypectomy syndrome: This syndrome occurs in roughly 1 in 1,000 colonoscopies and is most likely to occur when electrocoagulation (cautery or burning) is used to stop bleeding at the base of a polyp when it's being removed. Symptoms include fever and abdominal pain.
  • Medication side effects: An adverse reaction (e.g., nausea or vomiting) or rarely, an allergy, to the pain or sedative medications used during a colonoscopy may occur.

Purpose of Colonoscopy

A colonoscopy may be performed as a screening test to look for evidence of precancerous polyps or cancer, or as a diagnostic test when certain colon-related symptoms arise.

Screening Colonoscopy

While most screening tests are done in an attempt to find cancer in its earliest stage (referred to as early detection), a colonoscopy offers something more unique: It allows for a polyp to be detected and removed before it even has time to develop into a cancerous tumor.

The American College of Gastroenterology recommends that screening begin at age 45 for those at average risk for developing colon cancer. A screening colonoscopy is recommended every 10 years as long as results are normal.

Screening is recommended at a younger age (and more often) for those who have risk factors for colon cancer, such as:

Besides undergoing a colonoscopy every 10 years (or earlier, depending on a person's prior test results and risk profile), there are other colon cancer screening options, including:

Your healthcare provider may recommend one over another depending on several factors. Insurance coverage of such tests (as screening tools) can vary depending on your plan and health history.

Diagnostic Colonoscopy

A diagnostic colonoscopy may be recommended for those who have colon-related symptoms or signs that may indicate an underlying disease process, such as colon cancer, hemorrhoids, diverticular disease, or IBD.

Symptoms and signs that often warrant a diagnostic colonoscopy include:

How to Prepare

Once your colonoscopy is scheduled, your doctor will give you various preparatory instructions, such as:

  • Starting a low-fiber diet several days before the procedure
  • Drinking only clear liquids the day before the procedure
  • Avoiding any liquids with red, purple, or blue dyes (which may stain the colon and interfere with the test)
  • Stopping certain medications (nonsteroidal anti-inflammatory drugs or anticoagulants) for a period of time before your procedure, based on your individual bleeding and blood-clotting risks
  • Arranging to have someone drive you home after the procedure

To thoroughly clean out your colon, your doctor will have you undergo a bowel preparation, typically with a liquid laxative like Golytely (polyethylene glycol). While there are different types of bowel preparations, they all cause several hours of watery diarrhea, so be sure you have easy access to a bathroom.

What to Expect on the Day of Your Procedure

A colonoscopy takes about 30 minutes to complete.

Here is a brief summary of what you can expect from start to finish:

  • After you change into a hospital gown, a nurse will take your vitals and place an IV line in your arm or hand.
  • Once in the procedure room, you will be asked to lay on your left side with your knees bent. Sedative and pain medications will then be given, either in pill form or through your IV. This type of anesthesia is called "twilight sleep" and 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 advancing the instrument upward through your colon. To get a clearer view, air will be pumped through the colonoscope to open up the intestinal passage. If you are awake, you may feel some cramping or bloating during this time.
  • If any abnormal regions are noted, a biopsy may be performed using a special tool on the colonoscope. If polyps are found, they can be removed with a special wire loop on the scope. You will not feel anything during a biopsy or polyp removal.
  • When the procedure is finished, the healthcare provider will remove the colonoscope and you will be taken to a recovery area.


As your sedative wears off, you will be observed in a recovery area for about one hour. You may wake up shortly after the procedure or be drowsy for some time. Because of the sedative medications used, most people don't remember the test.

When you are awake and alert, your IV will be removed and your nurse will likely offer you some food (such as crackers and juice) before going home.

Keep in mind, you may feel drowsy for the first 24 hours after your colonoscopy, so you 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, like signing legal documents, until the day after their procedure.

While you will be able to resume most ordinary daily activities and your regular diet right after a colonoscopy, you should avoid alcohol and strenuous activities for at least 24 hours.

When to Seek Medical Attention

Mild bloating, gas pains, or even a small amount of blood with your first bowel movement are normal after a colonoscopy. But be sure to contact your doctor if you experience any of the following symptoms:

  • Fever or chills
  • Passing frequent stools with blood or blood clots
  • Abdominal pain, swelling, or hardening
  • An inability to pass gas
  • Nausea and vomiting
  • Dizziness or feeling faint
  • Trouble breathing, leg swelling, or chest pain

Long-Term Care

Any potential follow-up care will depend on the results of your colonoscopy, which you should receive or hear about within seven to 10 days of undergoing the procedure.

Remember to follow up after your test. Do not assume everything is OK if you do not hear back from your doctor.

Once you get your results, if your colonoscopy is completely normal and you have an average risk of developing colon cancer, a follow-up colonoscopy will generally be recommended in 10 years.

On the other hand, if a polyp or abnormal tissue is found and removed, it will be sent off to a pathologist for evaluation to determine if its cancerous, precancerous, or noncancerous.

Based on your results, a repeat colonoscopy may be recommended in one to 10 years, depending on various factors such the number of polyps found and their size and type.

If cancer is detected, you will need to follow up with an oncologist for colon cancer staging and a treatment plan. Likewise, other medical conditions, such as inflammatory bowel disease, may warrant close follow-up with a gastroenterologist and/or additional testing.

A Word From Verywell

Indeed, undergoing a colonoscopy is not something most people look forward to. It is, however, an incredibly useful screening and diagnostic tool—one that is very safe and straightforward overall. As it can catch a polyp before it has the chance to become cancerous, a colonoscopy can also be life-saving. Stick to the screening guidelines set out by your doctor.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.