Colonoscopy is a painless screening test that checks for abnormalities in the large intestine (colon) and rectum. Growths in the intestine (polyps) and abnormal tissue found during the procedure are removed right then, possibly preventing cancer from developing. Colonoscopies are recommended beginning at age 50 as a screening for colorectal cancer. A colonoscopy may be recommended for stomach pain, chronic constipation, chronic diarrhea and rectal bleeding.

what to expect

Before a colonoscopy, you will need to avoid solid food the day before (you can drink only clear liquids) and you will need to fast completely the night before. You’ll also have to take a liquid or pill laxative the night before (and possibly the morning of the exam, too) to clean out your colon. Your doctor might also recommend avoiding any medications.

Here are the instructions for different types of colonoscopy preparations:

During the colonoscopy, you’ll receive medication either in pill form or via a needle in your arm (IV) to sedate you and make you comfortable during the procedure. Then a long tube (colonoscope) is inserted into your rectum and colon. The tube has a light and camera so your doctor can see inside your colon on a monitor. To get clearer images, your doctor can pump air into your colon through the tube, which may cause some cramping. Your doctor can insert instruments through the tube to take tissue samples (biopsy) or to remove polyps and abnormal tissue. 


The whole procedure takes 20 to 60 minutes, after which you’ll be in a recovery room for an hour or two while the sedation wears off. You’ll need someone to accompany you to the exam and drive you home. Afterward, you may have gas or feel bloated. Your doctor may give you instructions for aftercare, including any temporary dietary restrictions. The first time you go to the bathroom after the test, you may see a small amount of blood. That’s normal, but if it continues or you have a fever or stomach pain, call your doctor.

Results of the test can be:

  • Negative: There were no abnormalities detected, and you don’t need another colonoscopy for 10 years unless you have risk factors for colon cancer.
  • Positive: Polyps or abnormal tissue are detected. In that case, polyps will be checked in the lab to see if they’re noncancerous (benign), precancerous or cancerous (malignant). You might need surgery if abnormal tissue or polyps were found and couldn’t be safely removed during the procedure. Depending on the findings, you might need screenings more often.

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