What is it, and what is it for?

A colonoscopy test is a flexible camera test of the large bowel (‘colon’).  It is a simple diagnostic procedure that takes around 30 minutes, and the vast majority of patients will go home the same day.  It involves passing a flexible telescope through the back passage, and gently manoeuvring it around the colon to the very top – around 70 centimetres – before carefully inspecting the bowel while slowly withdrawing the camera.

Colonoscopy is a useful test for investigating symptoms such as a change in bowel habit, diarrhoea, rectal bleeding, and occasionally it is done to investigate abdominal pain.  Sometimes small tissue samples are taken (‘biopsies’) with tiny forceps, which does not cause any discomfort.  When small growths of extra tissue (‘polyps’) are seen they can also be removed with the camera, which should also be painless.  Occasionally narrowings in the bowel are seen, usually due to chronic inflammatory conditions such as Crohn’s disease, and these can be stretched (‘dilated’) using a small balloon to help alleviate symptoms.  Rarely, stents (wire metal tubes) can be passed through cancerous narrowings to improve symptoms, either prior to or instead of a surgical operation.

What are the alternatives?

Colonoscopy is the ‘gold standard’ test for examining the large bowel.  There are two alternative tests.  The first is a more limited camera test called a flexible sigmoidoscopy, at which a flexible camera is passed to one third of the way around the colon.  It has the advantage of requiring less preparation before the test (see below) and being quick, but problems can be missed in the part of the colon which has not been examined.   The other test is called a CT pneumocolon, or ‘virtual colonoscopy’, and is a type of x-ray test.  Although less invasive than a colonoscopy it does require similar preparation (see below) and also involves a significant dose of radiation.  If anything is found it is not possible to take biopsies (see above), and a colonoscopy would then be required.

Is there anything I need to do before the test?

It is very important that the bowel is clear prior to a colonoscopy so that problems are not missed.  This requires dietary modification (low fibre diet for 2 days before hand) and strong laxatives taken on the day prior to the test.  An information sheet and the laxatives will be given to you following the clinic appointment with full instructions explaining what to do.  You will start to go the toilet frequently on the afternoon and evening prior to the test and you will need to be near a toilet.  This may make being at work inconvenient.  This will continue during the night and on the morning of the procedure.  If you take blood-thinning medications such as warfarin or clopidogrel, or are diabetic, the doctor will give you some specific advice when you see him in clinic about what to do with your tablets.

What will I feel during the test?

The test is usually performed under mild sedation.  This requires a needle in the arm and an injection of a painkiller and a mild sedative.  You will be awake but drowsy.  You may still feel some wind and bloating, and at times some mild discomfort but in general colonoscopy is rarely a painful test.   A minority of patients prefer to have no sedation, particularly if they need to drive a car within the subsequent 24 hours, and it is perfectly possible to have the test without sedation.

What happens after the test?

After the test you may feel slightly drowsy for an hour or so if you have had sedation.  Although you may feel  normal after this the drugs are still in your system for 24 hours and you should not drink alcohol, drive a car, go swimming, sign legal documents etc. within this period.  You may feel bloated after the test – this passes fairly quickly.  You can get back to eating and drinking as normal as soon as you feel up to it.  Usually patients will be allowed to go home an hour or so after the test when they are feeling awake enough and have had something to eat and drink.

Are there any risks?

Colonoscopy is a very safe diagnostic procedure and the risks, although present, are tiny.  The main serious complication is damage to the bowel wall, or ‘perforation’.  This can occur after a routine diagnostic procedure but is incredibly rare, well under 1 in 1000 procedures.  The risk is higher if large polyps have been removed from the bowel wall, with a risk of up to 1 in 1-200 following removal of the largest polyps, or after stretching (‘dilatation’) of narrowings (‘strictures’) or colonic stent insertion – again with a risk of around 1 in 100.  A perforation might be suspected if there is significant pain following the procedure which is not getting better.  If suspected, a CT scan would be performed, and the patient may be kept in overnight.  If confirmed, an operation may be required although a small perforation may seal itself with bowel rest and antibiotics.  The second main risk is of bleeding.  This is vanishingly rare following a diagnostic procedure, but there is a risk following removal of polyps – up to 1 in 100 for large polyps.  Although it can occur at the time of polyp removal, in which case the consultant can stop the bleeding with the camera, it may occur up to 10 days following the procedure, and if the bleeding is significant you must let the hospital or consultant know immediately.  Out of hours you may have to go to your nearest casualty department.