Colonoscopy

What is a colonoscopy?

A colonoscopy is a test to check for disease inside your colon and rectum. Your colon and rectum make up the lower half of your gut and are often called your bowel.

During a colonoscopy, a doctor puts a tube with a camera on the end (a colonoscope) into your bottom (anus) and passes it up through your rectum and colon. This allows your doctor to look for problems such as cancer, infl ammation (red, swollen patches) or polyps (small lumps, like cherries, on the inside wall of your bowel).

If your doctor sees anything unusual during the test, he or she can take samples of tissue to look at more closely. This is called a biopsy.

What happens during a colonoscopy?

You have a colonoscopy in hospital, but you can usually go home the same day. The test is done in an operating theatre, usually by a doctor trained in problems of the digestive system (a gastroenterologist). But it's not an operation and you won't have a scar or stitches afterwards.

How well does a colonoscopy work?

A colonoscopy is a good way to test for cancer in your colon or rectum. The doctor can look through the whole of your lower bowel in one test.[6]

• A colonoscopy is more than 98 percent accurate at spotting cancer and large polyps. This means that the doctor will see cancer in more than 98 in 100 people who have it.[7] [8] [9] [10] But the test can miss cancer. This happens to about 2 in 100 people. In some studies, doctors miss cancer more often than this.[11]
• It's very unlikely that you'll be told you do have cancer when you don't.[7] [8]

Most people who have a colonoscopy don't have cancer. More often, doctors find one of the following:[7] [12]

• Nothing, jus t a normal bowel: This is very common. In one study, the bowel looked normal in a third of people who had bleeding from their anus and three-quarters of the people with bad diarrhoea.[12]
• Polyps: These are small lumps on the inside wall of your bowel. They aren't cancer. But some polyps eventually turn into cancer. A colonoscopy will find polyps that are at least 1 centimetre (about half an inch) across in about 98 percent of people who have them. But the test may miss polyps that are smaller than 5 millimetres (a fifth of an inch) across in about a quarter of people.[13] [14] In one study of more than 9,000 people who had a colonoscopy, about a quarter of them had polyps.[15]
• Inflammati on: Sore-looking patches or ulcers inside your bowel can be a sign of colitis. Colitis means the lining of your colon is inflamed (red and swollen) in places. It's also called inflammatory bowel disease. In one study, 1 in 10 people had inflammatory disease.[16]
• Weaknesses in the wal l of your gut: Weak areas can balloon outwards to form tiny pouches. Doctors call this divert icular disease. It's very common and often harmless. In the study of more than 9,000 people having a colonoscopy, more than 1 in 10 had diverticular disease.[15]
• Piles (haemorrhoids): These can make your bottom itchy and sore. They may also hurt or bleed.

What are the risks of a colonoscopy?

For most people, colonoscopy is simple and safe.[15] Colonoscopy is also safe for older people. Only 1 in 2,000 people over 65 get complications.[17]

But you may find clearing out your bowel unpleasant or inconvenient. Strong laxatives can give you diarrhoea. Drink plenty of clear fluids such as water, clear fruit juice or clear soup to keep hydrated.[3] In one study, some people said they lost sleep rushing to the toilet all night. A few people said they couldn't control their bowels and had accidental bowel movements or leaks.[18]

Things don't often go wrong during a colonoscopy. In one study of more than 3,000 people, six had serious bleeding and four had other serious complications.[19]

Here are the things that could happen.

Not being able to see all your bowel: Your bowel is long with lots of twists and turns, so sometimes it's difficult to feed the colonoscope all the way up. In studies, this happens to between 3 and 7 out of 100 people.[12] [20] [21] This is usually because the person was uncomfortable, there were loops in the bowel or the bowel wasn't clear. If it happens, you can have a different test or another colonoscopy later.[12]

Breathing or heart problems: Sedatives and pain killers can affect your breathing and your heart. But serious problems are rare because your breathing is monitored during the colonoscopy. Your blood pressure may be monitored too.

Damage to the bowel: The colonoscope may poke a hole in the wall of your bowel. Doctors call this a perforation. A summary of the research found that it can happen to between 3 and 60 in every 10,000 people.[22] But it's a serious problem that causes inflammation inside your abdomen. If this happens, you'll probably need an operation to sew up the hole.

Bleeding: You may bleed from your bottom after a colonoscopy. This is more likely to happen if you've had a sample of tissue or polyps removed. You may need to go back into hospital to stop the bleeding. A summary of the research found this happens to between 2 and 30 in every 1,000 people who have tissue removed during a colonoscopy.[22] In one study of almost 2,000 people having a colonoscopy, three people had bleeding so bad that they had to go to the hospital emergency department.[19]

Allergic reactions: You may be allergic to the sedative. This can affect your breathing and your heart. Before you have a colonoscopy, it's important to tell your doctor if you have any allergies.

Death: This is unlikely. A summary of the research found between 1 in 30,000 and 1 in 3,000 people died because of something related to their colonoscopy.[22]

What are the alternatives to a colonoscopy?

If you have blood in your stools, some hospitals in the UK recommend a test called a barium enema. For this test, your bowel is filled with a dye that helps shows any cancer, polyps or weaknesses in your bowel (diverticular disease) on an X-ray.[6] The test is done in hospital by trained doctors called radiologists. It isn't as good as a colonoscopy at spotting cancer, but there are fewer risks.[11] This test detects bowel cancer in between two-thirds and all people who have it.[23]

Some people have a barium enema, then a colonoscopy. For example, if your barium enema showed up a polyp, you might have a colonoscopy to have the polyp removed.

Sigmoidoscopy is another test to look inside your bowel. It's like a colonoscopy, but uses a shorter tube. So it's only useful for looking inside your rectum and the lowest part of your colon (called the sigmoid colon). The doctor may use a flexible sigmoidoscope which allows him or her to look around bends in your colon and to go further up. It's also more comfortable for you. This test finds up to two-thirds of polyps and cancers.[24] You may have a sigmoidoscopy if you have:

• Bright red bleeding from your anus, not the darker bleeding that looks like it comes from higher up in your bowels
• Pain in the left side of your abdomen. This means you are more likely to have colitis or diverticular disease than cancer.

A CT colonography is a new test. It's sometimes called virtual colonoscopy. Doctors use a type of X-ray machine called a CT scanner to take pictures of your bowel rather than putting a colonoscope into it. You won't usually need a sedative, but you'll probably need to take laxatives to clear your bowel.

A CT colonography may be quicker and more comfortable than a colonoscopy.[25] But we don't know for certain whether it's as accurate.[26] In a review of 14 studies, CT colonography found polyps that were at least a centimetre across in about 9 in 10 people who had them.[27] But in another study, CT colonography only found these polyps in 6 in 10 people who had them.[7] Flat growths or areas of damaged tissue are sometimes missed.[28]

If the test finds polyps or suspected cancer, you'll need to have a colonoscopy and biopsy to remove them.

The National Institute of Health and Clinical Excellence (NICE) says that a CT colonography is safe and works well enough to use in the NHS.[25] Frail or elderly patients may prefer this more comfortable colon test. CT colonography may also be suggested if a colonoscopy didn't see all of your bowel.[29]

What will happen afterwards?

You'll come round from the sedative about an hour after the colonoscopy. You shouldn't have any pain, but you may feel bloated and uncomfortable for a short time because of the extra air in your bowel. You may not remember much about the test because of the sedative.

As soon as you feel awake and comfortable, you can go home. You should make sure there's someone who can look after you for the next 24 hours.

You won't be able to drive if you've had a sedative, so you'll need someone to help you get home.

The doctor may tell you what they saw before you go. But if they took any samples of tissue, you'll have to wait a few days for the results. Sometimes, the hospital sends your results to your GP. But some people have to come back to the hospital for their results.

If you've had a biopsy or a polyp removed, you may have blood in your stools for a few days. If you had a polyp, you'll need at least one more colonoscopy, a year to five years later, to check for more polyps. You may need to have a colonoscopy every few years.[30]