Patient information from BMJ

Colonoscopy

Last published:Jul 03, 2020

A colonoscopy is a test that allows a doctor to look inside your bowel. This information covers how and why it’s done, any risks involved, and what to expect afterwards.

You can use our information to talk with your doctor if you have any questions about having this test. 

What is a colonoscopy?

Some medical conditions affect the lower part of your digestive system, including the rectum and colon (you might hear it called your bowel). A colonoscopy is a test that allows a doctor to look inside your rectum and colon for possible problems.

During a colonoscopy, a doctor inserts a tube with a camera on the end (a colonoscope) into your anus and passes it up through your rectum and colon.

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. 

Why might I need a colonoscopy?

The main reason for having a colonoscopy is if you have been having symptoms that suggest a problem with your colon.

The main symptoms that suggest a problem are: 

• blood in your stool (poo) when you go to the toilet. You might notice blood in the toilet bowl, on the toilet paper, or covering the stool

• a change in your bowel habits, such as having bowel movements more often each day or having diarrhoea

• having constipation that doesn’t get better, along with other symptoms. 

A colonoscopy can check for signs of conditions such as:

• cancer of the colon or rectum (sometimes called bowel cancer)

• Crohn’s disease, which causes inflammation (swelling) in the digestive system

• diverticulitis, which causes small pouches to appear in the digestive tract. These can sometimes become infected or swollen

• diverticular disease, where tiny pouches in the colon wall can sometimes cause pain and discomfort

• ulcerative colitis, which causes inflammation and ulcers in the colon

• polyps, which are small lumps on the inside of your bowel. Polyps are not cancer, but they can sometimes turn into cancer. So it’s best to remove them when they’re found. 

Just because you have some symptoms that can be caused by these conditions doesn’t mean that you have one of them.

This is because these symptoms can also be caused by something fairly harmless, such as haemorrhoids. Haemorrhoids (you might hear them called piles) are swollen veins just inside the anus.

Not everyone with the symptoms listed above needs a colonoscopy. Your doctor will probably only suggest this test if: 

• you're over 40 and you've had bleeding and other symptoms above for at least six weeks

• you're over 60 and you've had one or more of these symptoms for at least six weeks. This is because older people are at greater risk of cancer. If you have bleeding, your doctor will ask if you have any itching around your anus. Itching or soreness around your anus are more likely to be caused by haemorrhoids than by cancer

• you or your doctor can feel a lump in your abdomen, or your doctor can feel a lump in your rectum when he or she examines you internally

• you've had polyps before, or you have a family history of bowel cancer

• a blood test shows that you have anaemia (not enough iron in your blood). It can be a sign that you are slowly losing blood from your bowel, but not enough to see in your stools

• you've had another test, such as a barium enema, that shows that you have a problem in your bowel. 

In many countries, once you reach a certain age (for example, in the UK it’s 60) you will be invited to have bowel cancer screening. You can do this test at home with a kit that you will be sent. You then send the kit to a lab to be tested.

But bowel cancer can sometimes happen to people younger than 60. Most people who have symptoms don’t actually have cancer. But this test can check. 

What will happen?

Before the colonoscopy

A colonoscopy is done in hospital, but you can usually go home the same day. It's not an operation and you won't have a scar or stitches afterwards. But you do need to prepare for it.

The main thing you need to do is to clear out your bowel using a laxative, usually at home the day before the procedure. Your nurse will give you instructions about how to do this. These instructions will cover: 

• how to take the laxative

• what you can and cannot eat and drink in the day or two before the test, and

• how long before the test you need to stop eating and drinking. 

During the colonoscopy

You’ll need to undress and put on a hospital gown. You might be offered a sedative medication to help you relax. But you’ll be awake during the procedure. You then lie on your side with your knees pulled up towards your chest.

During the procedure, the doctor: 

• will insert a flexible tube (the colonoscope) into your bowel by feeding it up through your anus. The colonoscope has a light and a camera on the end. While feeding the colonoscope through your bowel, the doctor watches the screen and checks for anything unusual

• can use the colonoscope to remove any polyps found during the test

• can take small samples of tissue for a biopsy. It's done by passing an instrument down a hollow tube built into the side of the colonoscope. The instrument has tiny clippers on the end for cutting away a small piece of tissue. This shouldn’t hurt. But let someone know if it does. 

A colonoscopy can be uncomfortable and embarrassing, but it shouldn't hurt. If you do feel pain, it's important to tell the doctor or nurse.

Some people find that they can't control their bowels during the test. This is normal. It's just your bowel reacting to the tube inside it. 

What are the risks?

Colonoscopy is a common procedure, and complications are rare. For most people, the worst things about it will be the diarrhoea caused by the laxative and the embarrassment of the test itself.

But, as with any medical procedure, complications do sometimes happen. These include:

• the doctor being unable to see all of 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. This can happen if the person is uncomfortable, there are loops in the bowel, or the bowel isn't clear. If it happens, you can have a different test or another colonoscopy later

• breathing or heart problems. Sedatives and painkillers can affect your breathing and your heart. But serious problems are rare because your breathing is monitored during the colonoscopy

• damage to the bowel: The colonoscope can poke a hole in the wall of your bowel. Doctors call this a perforation. 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. But it's not common

• bleeding. You might bleed from your bottom after a colonoscopy. This is more likely if you've had a sample of tissue or polyps removed. Some people need to go back into hospital to stop the bleeding

• an allergic reaction to the sedative. This can affect your breathing and your heart. It's important to tell your doctor before the test if you have any allergies. 

What can I expect afterwards?

The sedative wears off about an hour after the colonoscopy. You shouldn't be in any pain, but you might feel bloated and uncomfortable for a short time. This is because having a colonoscopy can cause there to be extra air in your bowel.

As soon as you feel awake and comfortable, you can go home. You should make sure there's someone with 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 might tell you what he or she was able to see with the colonoscope before you go home. But if he or she took samples of tissue, you'll have to wait a few days for the results. If you've had a biopsy or had a polyp removed, you might have blood in your stools for a few days. If you had a polyp, you'll need at least one more colonoscopy, between one and five years later, to check for more polyps. You might need to have a colonoscopy every few years. 

Your test results

A colonoscopy is a useful test for finding problems, including bowel cancer. But most people who have this test don’t have cancer.

It’s likely that the results of your colonoscopy will show one of the following: 

• a normal bowel. This is very common. Some people have bleeding from their anus or irregular bowel habits even if their bowel looks normal

• polyps. This is very common. Polyps aren't cancer. But some polyps can turn into cancer, so your doctor will remove them if he or she finds them during the test

• inflammation. 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

• weaknesses in the wall of your gut. Weak areas can balloon outwards to form tiny pouches. Doctors call this diverticular disease. It's very common and often harmless

• haemorrhoids (piles). These can cause itching, pain, and bleeding, but they’re not usually a serious problem. 

You can discuss the results of your colonoscopy with your doctor, and talk about any treatments that might help you.