What is a colonoscopy?

A colonoscopy is a procedure during which a flexible tube, known as a colonoscope, is inserted into the anus and through the rectum so it can view the inside of the large bowel (the colon). This tube transmits images to a screen where signs of a medical condition can be seen.

The colonoscope is about half the thickness of an electrical cord. It has a camera and light so that the bowel can be viewed in detail.

It is flexible and can be turned around curves, allowing it to travel through the length of the colon.

When is a colonoscopy recommended?

A colonoscopy may be recommended by a gastroenterologist, a specialist who can diagnose and treat conditions of the gut, to investigate unexplained changes in bowel habits.

People usually have a colonoscopy:

  • to identify the cause of gut-related problems such as abdominal pain or bleeding from the anus
  • if they have had a positive bowel cancer screening test (poo test)
  • if they have a high risk of illness due to chronic bowel disease or a family history of bowel disease such as bowel cancer
  • to identify the cause of unexplained weight loss
  • following a recommendation from a previous colonoscopy

When should I have a colonoscopy as a screening test?

A colonoscopy is the best way to diagnose and prevent bowel cancer and for most people, it is a straightforward test. However, as with most medical tests, complications may occur. I f you are at average or slightly above average risk of bowel cancer, a fecal occult blood test (poo test) is used for screening rather than a colonoscopy.

Colonoscopy Surgery

How to prepare for a colonoscopy?

Bowel preparation is not pleasant but essential for an accurate and safe colonoscopy. If you need to have this procedure, you will be given detailed instructions on each stage of the bowel preparation which will take into account your individual needs.

A complete bowel preparation involves:

  • modifying your diet — this may start several days before your colonoscopy and you will have clear instructions on what you can and cannot eat
  • taking a bowel preparation (a strong laxative) — your specialist will recommend the right one for you
  • increasing your fluid intake — you will be given specific instructions on the type and amount of fluids to have leading up to your examination

The bowel preparation will cause diarrhea so it should be done while at home with easy access to the toilet.

The area around the anus may become irritated by diarrhea. Showering, and using moist wipes instead of toilet paper, may ease this discomfort.

It is important to drink only clear fluids on the day before and to not eat solid foods or dairy products like milk. You will be allowed to have fluids like water, clear fruit juice (apple, white grape, white cranberry), tea or coffee (no milk), clear carbonated drinks, or clear soup. You will be asked not to have anything further to eat or drink for a period of time before your procedure — this will be included in the bowel preparation instructions you received.

You might have some minor side effects from the bowel preparation, including:

  • nausea
  • bloating
  • abdominal distension
  • shaking chills if the preparation has been in the fridge

If you experience any minor side effects take a short break and then start taking the bowel preparation again.

More serious side effects include:

  • dizziness
  • fever
  • severe headache

The more serious side effects might indicate dehydration or an allergic reaction to the bowel preparation. Contact your specialist or GP if you have any serious side effects or if you can not finish the bowel preparation.

If you take regular medicines, talk to your doctor well before you start taking the bowel preparation. Some medicines should be taken as normal, and some can be delayed. It is particularly important to talk to your doctor if you take blood-thinning medicines.

What happens during the procedure and straight after?

The colonoscopy lasts for between 25–45 minutes. Most people have mild anesthetic or sedation to minimize any pain or discomfort. The sedation also means you may remember nothing or very little of the procedure.

During the procedure

You will be positioned on your left side and given sedation before the colonoscope is passed into the colon. The colonoscope is inserted at the end of the large intestine and then withdrawn slowly so the lining of the colon can be examined again.

Air is also pumped into the colon to help the doctor examine the lining carefully. During the procedure, polyps (small tissue growths that might develop into cancer) may be removed and small tissue samples (biopsies) may be taken and sent to the laboratory to determine what type of disease is present.

The procedure is usually performed as day surgery and you will be monitored in recovery for an hour or two after the procedure until the sedation wears off.

After the procedure

Afterward, you may feel drowsy and will need to arrange for somebody to help you get home. It is also recommended that you arrange to have someone stay with you the night after your colonoscopy.

Straight after the sedation, you should not:

  • drive a car
  • travel on public transport alone
  • operate machinery
  • sign legal documents
  • drink alcohol

You should expect to make a full recovery the next day.

Your doctor will give you a brief report on what they saw, but you probably won’t get full results and further advice until later at a follow-up appointment. Your doctor or nurse will also give you instructions on how to look after yourself at home, including:

  • when to re-start any regular medicines
  • diet instructions
  • what to do if you have any problems

Are there any risks or side effects?

Complications during or following a colonoscopy are rare. However, the potential risks of the procedure include:

  • bleeding
  • infection
  • intestinal perforation (when the colonoscope pokes a hole in the bowel)

The combination of bowel preparation and sedation may cause tiredness and weakness following the procedure which will pass if you rest and drinking plenty of fluids.

A colonoscopy can have minor side effects can occur, but they usually pass within a few hours of the procedure. These include:

  • abdominal bloating
  • gas
  • passing a small amount of blood if polyps or tissue samples were taken although this is rare

If you experience any of the following signs or symptoms up to 14 days after the colonoscopy, you should contact your specialist or GP immediately:

  • severe abdominal pain or bloating
  • persistent nausea or vomiting
  • black, tar-like poo
  • persistent bleeding from the anus
  • fever or chills
  • any other symptoms that concern you

Other questions you might have

Are there alternatives to a colonoscopy?

There are other less commonly used diagnostic tests, such as virtual colonoscopy, or flexible sigmoidoscopy.

Virtual colonoscopies use an MRI or CT scanner. They create images of the colon and the rectum on screen. These tests are not as accurate as a colonoscopy because tissue samples cannot be taken and smaller abnormalities may not be seen.-If the images show any abnormalities you will need to have a colonoscopy because polyps and biopsies cannot be done during a virtual colonoscopy. A flexible sigmoidoscopy test is used to investigate the rectum and lower part of the colon only.

Are there any side effects of a colonoscopy?

The only side effect is temporary discomfort as a result of trapped wind and flatulence, caused by air that may have been introduced to the colon during the procedure.

What happens if the colonoscopy can’t be completed?

If the colonoscopy is not successfully completed it may need to be repeated.


National Bowel Cancer Screening Program (About colonoscopy)Bowel Cancer Australia (Colonoscopy)Cancer Council (Colonoscopy)Gastroenterological Society of Australia (GESA) (Colonoscopy fact sheet)

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