Tests for bowel cancer

You usually have a number of tests to check for bowel cancer. The tests you may have include:

  • a test that looks for blood in your poo. This is a Faecal Immunochemical Test (FIT)
  • looking at the whole of the inside of your large bowel using a flexible tube (colonoscopy) or to look at the lower part of the bowel (sigmoidoscopy)
  • scans

Bowel (or colorectal cancer) means cancer that starts in the large bowel (colon) or the rectum (back passage). This is different from cancer that starts in the anus or small bowel.

Diagram showing the position of the small bowel

Tests your GP might do

Most people with symptoms that could be due to cancer start by contacting their GP surgery. Your first appointment may be a telephone appointment. Your GP surgery then might arrange for you to go in and see a doctor or other healthcare professional.

Tests your GP might do include:

  • a test that looks for tiny traces of blood in a sample of poo (FIT)
  • an examination of your rectum and tummy (abdomen)
  • blood tests

Your GP may also ask you for another sample of poo (stool) to check for inflammation in the bowel. This test is called Faecal Calprotectin. Your GP or practice nurse will give you a sample pot to take away with you. You then bring it back once you have collected the poo sample.

Testing for blood in your poo using FIT

FIT is a test that looks for tiny traces of blood in poo that are too small to see. Blood in poo can be caused by a number of medical conditions but it can also be a sign of bowel cancer.

You do this test yourself at home. Your GP will give you the test kit or they will arrange for you to get one in the post.

Examination of your rectum and abdomen

An examination of the rectum is also called a digital rectal examination (DRE). It involves your doctor feeling inside your anus and rectum using their gloved finger. They feel for any lumps or hard areas.

It’s normal to feel anxious about this test but it usually only takes a few minutes. You can ask for someone else to be in the room if you want, to act as a chaperone. This chaperone can be a friend or relative, or a health professional such as a practice nurse.

Your doctor may also feel your abdomen for any areas that are swollen or might not feel normal. And if you have any pain, they will feel those areas. They may also listen to your abdomen to find out if it sounds normal.

Blood tests

Blood tests can check your general health, including how well your liver and kidneys are working. Your doctor can also check the number of blood cells Open a glossary item such as red blood cells. 

Tests your specialist might do

Depending on the results of your examination and FIT, your GP might refer you to a specialist. You are usually referred to a lower gastrointestinal (lower GI) clinic where you might see a GI specialist nurse and a colorectal doctor.

Your specialist does more tests. These might include:

  • colonoscopy
  • flexible sigmoidoscopy
  • colon capsule endoscopy


A colonoscopy looks at the whole of the inside of your large bowel using a flexible tube called a colonoscope. The tube has a small light and camera at one end and your doctor can see pictures of the inside of your bowel on a TV monitor.

You usually have this test in the endoscopy department of the hospital. You need to take medications (laxatives) the day before your test to empty your bowel.

During the test, your doctor can take tissue samples (biopsies) of any abnormal areas. They send the biopsies to the laboratory to check for bowel cancer.

Click on the link above to watch an animation about having a colonoscopy.

Flexible sigmoidoscopy

A flexible sigmoidoscopy looks inside the lower part of your large bowel using a flexible tube. This is also called a bowel scope or flexi sig.

A flexible sigmoidoscopy is similar to a colonoscopy. But it only looks inside the rectum and lower part of your bowel, whereas a colonoscopy looks at the entire bowel.

Colon capsule endoscopy

A colon capsule endoscopy looks at the inside of your large bowel (colon) using a capsule that you swallow. The capsule is the size of a large pill. It has a small wireless camera that sends pictures of the inside of your bowel to a data recorder.

You might have a colon capsule endoscopy instead of a colonoscopy straight away. It can help to rule out bowel cancer. This test isn’t available in all hospitals at the moment. 

What tests do I need after being diagnosed with bowel cancer?

If you have a biopsy that shows that you have bowel cancer, you may have more tests to work out where and how big the cancer is. This is called staging the cancer.

The tests you might have include:

  • tests on your bowel cancer cells
  • CT colonography
  • CT scan
  • PET-CT scan
  • MRI scan
  • ultrasound scan of the abdomen and rectum

Tests on your bowel cancer cells

After a doctor removes tissue or cancer from your bowel, they send the samples to a laboratory. A doctor called a pathologist does various tests on the cells. These tests can help to diagnose bowel cancer and look for certain gene Open a glossary item changes.

Knowing about gene changes can help your doctor decide the best treatment for you. This is because certain treatments work better if you have certain gene changes.

Your doctor usually tests the cancer cells for changes in the following genes:

  • MSI
  • RAS
  • BRAF

CT colonography

CT colonography is a test that uses a CT scan to check the large bowel and rectum. CT stands for computer tomography. It uses x-rays and a computer to create detailed pictures of the inside of your bowel.

You need to have an empty bowel for this test, so you take medicines to empty your bowel the day before.

CT scan

You might have a CT scan of your chest, abdomen and the area between your hip bones (pelvis). This is to check where the cancer is and whether it has spread to other parts of the body.

PET-CT scan

A PET-CT scan combines a CT scan with a PET scan to give detailed information about the cancer. You might have a PET-CT scan to:

  • help decide the best treatment for you
  • show how well the treatment is working
  • check whether the cancer has come back

MRI scan

MRI stands for magnetic resonance imaging. It uses magnetism and radio waves to create pictures of the inside of the body.

You may have an MRI scan to find out where in the bowel the cancer is, how big it is and whether it has spread to any other part of your body.

Ultrasound scan

Ultrasound scans use high frequency sound waves to create a picture of a part of the body. They can show up changes including abnormal growths. You may have an ultrasound scan of your abdomen to check whether the cancer has spread.

You may also have an ultrasound scan of your rectum. An ultrasound scan of the rectum is also called trans rectal ultrasound scan (TRUS). You may have this if you have rectal cancer.  

Tumour markers

Tumour markers are substances that are produced by the cancer or other cells of the body in response to cancer or other conditions. They’re usually proteins that can be found in the blood, urine or body tissues.

Some tumour markers are only produced by one type of cancer. Others can be made by several types.

Doctors might use tumour markers to monitor how well your cancer treatment is working or check if the cancer has come back.

For bowel cancer, your doctor might test for a tumour marker called carcinoembryonic antigen (CEA).


All the tests you have help your doctor find out about the stage of the cancer.

This is important because doctors recommend your treatment according to the stage of the cancer.

Coping with bowel cancer

Coping with a diagnosis of bowel cancer can be difficult. There is help and support available to you and your family.

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