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Colonoscopy is an examination of the large intestine using a long thin flexible video endoscope. (sedation will be given by the anaesthetist during the procedure)


Direct visualization of : polyps, inflammation of bowel wall, abnormal blood vessels (angiodysplasia). 

Biopsies can be taken for histology. 

Most polyps can be removed and treated at the same time

 If there are haemorhoids, these can be banded at the same time. Banding is good at reducing bleeding from haemorrhoids and can reduce the size of prolapsing haemorrhoids. If there are already skin tags with associated haemorrhoids, these will not go away with banding. (The rubber bands are applied more than an inch inside the anal canal to reduce the pain and as such will not get rid of the skin tag/external haemorrhoids) After the banding, there can be discomfort, feeling of fullness/wanting to go to the toilet(like a severe constipation) and sometimes pain if the haemorrhoids are large. A local anaesthetic nerve block and Procosedyl suppository/Lignocaine gel is usually given to reduce the pain/discomfort. The bands usually fall off withing 2 weeks. Avoid sitting on the toilet and straining for too long after the banding. You need to take a high fibre diet and keep yours stools soft in the long term to reduce the risks of the haemorrhoids recurring.


Perforation - Hole in bowel(1 in 1000; risk incresased if larger polyp removed, adhesions/hysterectomy or cancer present): if so will need surgery

Serious bleeding from bowel(or more rarely bleeding from spleen where colon is attached) (1 in 1000) : may need blood transfusion or an operation. Minor bleeding from trauma to haemorrhoids/bowel wall.

Sepsis/infection; anaesthetic reactions; aspiration/pneumonia; heart attack/stroke; death(1 in 10000)

Incomplete colonoscopy(<5%) because of looping/angulation of bowel- will then need another method of investigation to view the rest of the colon eg Contrast enema or CT colonscopy


Incomplete view - Polyps may be missed / covered by faeculent fluid / faeces / mucosal fold (1-5%)

Other Investigations As Alternatives to Colonoscopy

1. Contrast (Barium) enema or CT colonoscopy - Advantages: not as invasive, less risks of perforation, shorter waiting time for investigation (especially in public hospitals) Disadvantages: poorer visualization of smaller polyps/mucosal abnormality, exposure to radiation, no views of rectum(need another more limited scope (sigmodoscopy) to look at rectum)

2. Faecal occult blood test - to screen for polyps and bowel cancer.

3. Faecal colon cancer DNA test  - this will be more common in future as technology improves and cost comes down

4. Capsule endoscopy - good for imaging the small bowel, especially with persistent bleeding or anaemia despite normal gastroscopy and colonoscopy


A colonoscopy enables the doctor to see the inside lining of your large bowel(colon). In order to get a good view, it is important that the bowel is thoroughly emptied and clean on the inside - otherwise the bowel wall on the inside may be partially covered by faeces.


1 week before colonscopy -

Discuss with your GP about stopping these medications - aspirin, clopidrogel(eg. Plavix, Iscover), dipyridamole(eg Asasantin, Persantin). (These medications increase the risk of bleeding especially if a biopsy needs to be performed during the colonoscopy)

5 days before colonoscopy - If you are taking warfarin(Coumadin, Marevan), this is usually stopped then. Again it is important to discuss this with your usual doctor and your surgeon. For some low-risk patients on warfarin, that is all that needs to be done. For high-risk patients(risk of stopping the anticoagulant), daily injections with low-molecular weight heparin may need to be given.

2 days before colonoscopy -

Take only low-residue foods eg white bread, white rice, eggs, potato without the skin. Do NOT eat vegetables, fruits or anything high in fibre(avoid any food with seeds in it!)

1 day before colonoscopy -

DRINK CLEAR FLUIDS ONLY after light dinner. Clear fluids include - water, black tea WITHOUT milk, clear fruit juices without pulps, clear soup, soft drinks, mineral water and cordial.

Take the 3 sachets of PICOPREP or Picolax(this can be purchased from a pharmacy) :

1. Mix the sachets of Picoprep with a glass of warm water

2. Take the Picoprep at 8pm, 10pm and midnight for a MORNING procedure(For an AFTERNOON procedure, take the prep at 10pm and then at 8am and 9am in the morning of the procedure)

Day of Procedure

REMEMBER to continue drinking at least a glass of water/clear fluids every hour.

You may have clear fluids UP TO 4 HOURS BEFORE the procedure.

Avoid coffee and alcohol as these can cause you to lose more fluids especially from your urine.

Day of Procedure

An anaesthetist will put in a drip and  give sedation during the procedure. 

After the colonoscopy, one will need to be observed in recovery.

Post-procedure : One may feel bloated/pass more flatus/pass small amount of blood(esp if biopsies taken)

Discharge advice

It is important to make arrangements ahead of time for someone to drive you home.  Do not drive or operate any machinery or sign any legal documents on the day of the colonoscopy/anaesthesia.

Immediately after the procedure, you may feel some addominal discomfort/cramps or bloating. You may also feel like passsing wind.(This is due to the air gently insufflated into your bowel during the colonoscopy)

A complete report will be forwarded to your doctor.

Should you have any bleeding, abdominal pain, black tarry stools or fever within 2 weeks after the procedure, you should contact your doctor immediately.

Click here for more detailed instructions on how to prepare for your colonoscopy

Dr LP Cheah also writes at for more Colonoscopy related information.