Skip to main content

Warning notification:Warning

Unfortunately, you are using an outdated browser. Please, upgrade your browser to improve your experience with HSE. The list of supported browsers:

  1. Chrome
  2. Edge
  3. FireFox
  4. Opera
  5. Safari

Diagnosis - Bowel cancer

If a GP refers you to a specialist because they think you could have bowel cancer, you'll have tests to check for cancer.

Tests for bowel cancer

There are 3 main types of tests you can get in hospital for bowel cancer:

  • flexible sigmoidoscopy
  • colonoscopy
  • computerised tomography (CT) colonography

A colonoscopy and CT colonography are used to get a more extensive examination of the colon.

Flexible sigmoidoscopy

A flexible sigmoidoscopy is an examination of your bottom and some of your bowel.

A sigmoidoscope is a long, thin, flexible tube with a very small camera and light. It's put into your bottom and up into your bowel.

The camera sends images to a screen.

A biopsy (small tissue sample) can be taken out when you are having a flexible sigmoidoscopy. The doctor will send it to a lab to check it.

It's better for your lower bowel to be as empty as possible when you have a sigmoidoscopy.

A sigmoidoscopy can feel uncomfortable. But it only takes a few minutes and most people go home straight after it.


When you have a colonoscopy, all of your bowel is examined with a colonoscope. This is like a sigmoidoscope but a bit longer.

Your bowel needs to be empty when you have a colonoscopy. The hospital will get you to eat a special diet for a few days beforehand. You'll take a medicine (laxative) to help empty your bowel on the morning of the examination.

The doctor will give you a sedative to help you relax during the test. They will put the colonoscope into your bottom and move it along the length of your bowel. Usually this is not painful. But it can feel uncomfortable.

The camera sends images to a screen. The doctor checks for any areas in the large bowel that do not look normal. This could be because of cancer.

A biopsy (small tissue sample) can be taken out when you are having a colonoscopy. The doctor will send it to a lab to check it.

A colonoscopy usually takes about 20 to 40 minutes. Most people can go home after they've recovered from the effects of the sedative.

You will probably feel drowsy for a while afterwards. You'll need to get someone to bring you home. Do not drive for 24 hours.

It's best for older people to have someone with them for 24 hours after the test.

In a small number of people, it may not be possible to pass the colonoscope completely around the bowel. They will then need to have a CT colonography.

CT colonography

CT colonography is also known as a virtual colonoscopy. A CT scanner takes 3D images of the large bowel.

The doctor will put a thin, flexible tube into your bottom. This is used to inflate your bowel with gas. CT scans are then taken from different angles.

You may need to have a special diet for a few days and take a laxative before the test. This is to make sure your bowels are empty when it's carried out. You may also have to take a liquid called Gastrografin before the test.

This test is for people who cannot have a colonoscopy because of other medical reasons.

A CT colonography is a less invasive test than a colonoscopy.

You may still need to have a colonoscopy or flexible sigmoidoscopy another time.

This is to:

  • remove any abnormal areas
  • take samples for a biopsy

Further tests

If you get a diagnosis of bowel cancer, your doctor may do more tests. This is to check if the cancer has spread from the bowel to other parts of the body. These tests also help your doctors decide on the most effective treatment for you.

These tests can include:

  • CT scan
  • MRI scan

CT scan of your tummy (abdomen) and chest

This is to check if the rest of your bowel is healthy and if the cancer has spread to the liver or lungs.

MRI scan

For people with cancer in the rectum this can give a clear image of the organs around it.

Stages of bowel cancer

After you have had all these tests, it's usually possible to decide on the stage of your cancer.

There are 2 main types of staging systems used for different types of cancer.

TNM staging system

The TNM system uses letters and numbers to describe the cancer. This system is used in different ways depending on the kind of cancer you have.

  • T - this describes the size of the tumour, with numbers 1 to 4 (1 for small, 4 for large)
  • N - this stands for lymph nodes, with numbers 0 to 3 (0 means no lymph nodes have cancer, 3 means many do)
  • M - this stands for metastases or whether the cancer has spread to another part of the body, with numbers 0 or 1 (0 means it has not spread, 1 means it has)

Number staging system

Bowel cancer is also staged by numbers. The stage describes the size of a tumour and how far it has spread.

The 4 main stages are:

  • stage 1 - the cancer is still contained within the lining of the bowel or rectum
  • stage 2 - the cancer has spread beyond the layer of muscle surrounding the bowel. It may have penetrated the surface covering the bowel or nearby organs
  • stage 3 - the cancer has spread into nearby lymph nodes
  • stage 4 - the cancer has spread beyond the bowel into another part of the body, such as the liver

Page last reviewed: 21 November 2023
Next review due: 21 November 2026