Diagnosis

When you first see your GP, they'll ask about your symptoms and whether you have a family history of bowel cancer.

They'll usually carry out a simple examination of your bottom, known as a digital rectal examination (DRE), and examine your tummy (abdomen).

This is a useful way of checking whether there are any lumps in your tummy or bottom (rectum).

The tests can be uncomfortable, and many people find an examination of their bottom a bit embarrassing, but they take less than a minute.

Your GP may also check your blood to see if you have iron deficiency anaemia.

Although most people with bowel cancer do not have symptoms of anaemia, they may lack iron as a result of bleeding from the cancer.

Hospital tests

If your symptoms suggest you may have bowel cancer or the diagnosis is uncertain, you'll be referred to your local hospital for a simple examination called a flexible sigmoidoscopy.

A small number of cancers can only be diagnosed by a more extensive examination of the colon.

The 2 tests used for this are colonoscopy or CT colonography.

Emergency referrals, such as people with bowel obstruction, will be diagnosed by a CT scan.

Those with severe iron deficiency anaemia and few or no bowel symptoms are usually diagnosed by colonoscopy.

Flexible sigmoidoscopy

A flexible sigmoidoscopy is an examination of your back passage and some of your large bowel using a device called a sigmoidoscope.

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

The camera relays images to a monitor and can also be used to take biopsies, where a small tissue sample is removed for further analysis.

It's better if your lower bowel is empty when you have a sigmoidoscopy so you may be asked to use an enema (a simple procedure to flush your bowels) at home beforehand.

It should be used at least 2 hours before you leave home for your appointment.

A sigmoidoscopy can feel uncomfortable, but it only takes a few minutes and most people can go home straight after the examination.

Colonoscopy

A colonoscopy is an examination of your entire large bowel using a device called a colonoscope, which is like a sigmoidoscope but a bit longer.

Your bowel needs to be empty when a colonoscopy is carried out, so you'll be advised to eat a special diet for a few days beforehand and take a medicine (laxative) to help empty your bowel before the examination.

You'll be given a sedative to help you relax during the test. The doctor will then insert the colonoscope into your bottom and move it along the length of your large bowel.

This is not usually painful, but it can feel uncomfortable.

The camera relays images to a monitor, which allows the doctor to check for any abnormal areas within the rectum or bowel that could be the result of cancer.

As with a sigmoidoscopy, a biopsy may also be carried out during the test.

A colonoscopy usually takes about an hour to complete, and most people can go home after recovering from the effects of the sedative.

You'll probably feel drowsy for a while after the procedure, so you'll need to arrange for someone to accompany you home.

It's best for elderly people to have someone with them for 24 hours after the test. You'll be advised not to drive for 24 hours.

Occasionally, it may not be possible to pass the colonoscope completely around the bowel. In this case, a CT colonography may be necessary.

Watch a video on what happens during a colonoscopy

CT colonography

CT colonography, also known as a "virtual colonoscopy", involves using a CT scanner to produce 3-dimensional images of the large bowel and rectum.

During the procedure, gas is used to inflate the bowel using a thin, flexible tube placed in your bottom. CT scans are then taken from a number of different angles.

As with a colonoscopy, you may need to have a special diet for a few days and take a laxative before the test to ensure your bowels are empty when it's carried out.

You may also be asked to take a liquid called gastrograffin before the test.

A CT colonography can help identify potentially cancerous areas in people who cannot have a colonoscopy because of other medical reasons.

It’s less invasive than a colonoscopy, but you may still need to have colonoscopy or flexible sigmoidoscopy at a later stage so any abnormal areas can be removed or biopsied.

Further information

• Association of Coloproctology of Great Britain and Ireland: bowel cancer symptom checker
• Lynn's Bowel Cancer Campaign: hospital tests
• Cancer Research UK: bowel cancer tests
• Macmillan Cancer Support: diagnosing colon cancer

Further tests

If bowel cancer is diagnosed, further tests are usually carried out to check if the cancer has spread from the bowel to other parts of the body. 

They also help your doctors decide on the most effective treatment for you.

These tests can include:

• a CT scan of your abdomen and chest – to check if the rest of your bowel is healthy and whether the cancer has spread to the liver or lungs
• an MRI scan – this can provide a detailed image of the surrounding organs in people with cancer in the rectum

Stages of bowel cancer

After all tests have been completed, it's usually possible to determine the stage of your cancer.

There are 2 ways that bowel cancer can be staged.

The first is known as the TNM staging system:

• T – indicates the size of the tumour
• N – indicates whether the cancer has spread to nearby lymph nodes
• M – indicates whether the cancer has spread to other parts of the body (metastasis)

Bowel cancer is also staged numerically. 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 and may have entered 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

Cancer Research UK has more information about bowel cancer stages.

Bowel cancer screening

In England, everyone aged 60 to 74 who's registered with a GP is eligible for NHS bowel cancer screening.

It involves using a home testing kit to send off some poo samples to be tested for blood.

This can help detect bowel cancer before symptoms appear, making it easier to treat and improving the chances of survival.

Find out more about bowel cancer screening

Page last reviewed: Mon Oct 2022 Next review due: Wed Feb 2020