Bowel cancer tests

Some people have tests for bowel cancer because they have symptoms. Others may not have any symptoms, but have a strong family history of bowel cancer or have received a positive result from a screening test.

To diagnose bowel cancer, your GP will examine you. This will include a digital rectal examination. They will refer you to a specialist for further tests.

The tests you have depend on your specific situation and may include:

  • general tests to check your overall health and body function
  • tests to find cancer
  • tests to see if the cancer has spread (metastasised).

The tests discussed in this section are used for diagnosing both early and advanced bowel cancer. The treatments are covered in separate chapters.

Some tests may be repeated during or after treatment to check how well the treatment is working. It may take up to a week to receive your test results. If you feel anxious while waiting for test results, it may help to talk to a friend or family member, or call Cancer Council 13 11 20 for support.

Learn more about:

General tests

The first tests you have are likely to be general tests. 

Physical examination

Your doctor will examine your body, feeling your abdomen for any swelling.

To check for problems in the lowest part of the bowel (anus and rectum), your doctor will insert a gloved finger into your anus and feel for any lumps or swelling. This is called a digital rectal examination (DRE).

The DRE may be uncomfortable, but it shouldn’t be painful. Because the rectum is a muscle, it can help to try to relax during the examination. The pressure on the rectum might make you feel like you are going to have a bowel movement, but it is very unlikely that this will happen.

Blood test

You may have a blood test to assess your general health and to look for signs that suggest you are losing blood in your stools.

The blood test may measure chemicals that are found or made in your liver, and check your red blood cell count. Low red blood cell levels (anaemia) are common in people with bowel cancer, but may also be caused by other conditions.

Bowel cancer tests

The main test used to look for bowel cancer is a colonoscopy.

Other tests that are sometimes used to diagnose bowel cancer include virtual colonoscopy and sigmoidoscopy.


A colonoscopy examines the whole length of the large bowel. It is still possible, however, that small polyps may be missed, especially if they are behind one of the many folds in the bowel or the bowel is not completely empty.

  • Before a colonoscopy, you will have a bowel preparation to clean your bowel. On the day of the procedure, you will probably be given an anaesthetic so you don’t feel any discomfort or pain. This will also make you drowsy and may put you to sleep.
  • During the procedure, the doctor will insert a flexible tube with a camera on the end, called a colonoscope, into your anus and up into your rectum and colon. Carbon dioxide or air will be passed into the colon. Your doctor will look for abnormal tissue (such as polyps), and take a sample (biopsy) for further examination.
  • A colonoscopy usually takes about 20–30 minutes. You will need to have someone take you home afterwards, as you may feel drowsy or weak.
  • An occasional side effect of a colonoscopy is temporary flatulence and wind pain, especially if air rather than carbon dioxide is passed into the bowel during the test.
  • More serious but rare complications include damage to the bowel or bleeding. Your doctor will talk to you about the risks.

Less commonly used tests

Virtual colonoscopy

This uses a CT or MRI scanner to create images of the colon and rectum and display them on a screen. It is also known as CT colonography.

  • A virtual colonoscopy is not often used because it is not as accurate as a colonoscopy and involves exposure to radiation. Your doctor may not be able to see small abnormalities and cannot take tissue samples.
  • Virtual colonoscopy is covered by Medicare only in some circumstances when a colonoscopy isn’t feasible.

Flexible sigmoidoscopy

This test allows the doctor to see the rectum and lower part of the colon (sigmoid colon) only. To have a flexible sigmoidoscopy, you will need to have an empty bowel. Before the test, you may be given a light anaesthetic.

  • You will lie on your side while a thin, flexible tube called a sigmoidoscope is inserted gently into your anus and guided up through the bowel. The sigmoidoscope blows carbon dioxide or air into the bowel to inflate it slightly and allow the doctor to see the bowel wall more clearly. A light and camera, at the end of the sigmoidoscope show up any unusual areas, and tissue samples (biopsy) can be taken.
Barium enema has been largely replaced by colonoscopy. Barium is a white contrast liquid that is inserted into the rectum and shows up any lumps or swellings during an x-ray.
Read more about sigmoidoscopy, colonoscopy and other tests

Further tests to see if cancer has spread

If any of these tests show you have bowel cancer, you will have additional tests to see if the cancer has spread to other parts of your body.


Your blood may be tested for a protein called carcinoembryonic antigen (CEA). This protein is produced by some cancer cells.

If blood test results show that you have a high CEA level, your doctor may organise more tests. This is because other factors, such as smoking or pregnancy, may also increase CEA levels. CEA levels may be retested after treatment to see if the cancer has come back.

CT scan

A CT (computerised tomography) scan uses x-rays to take many pictures of the inside of your body and then compiles them into one detailed, cross-sectional picture. A scan is usually done as an outpatient. Most people are able to go home as soon as the test is over.

  • Before the scan, dye is injected into a vein to make the pictures clearer. This dye may make you feel hot all over and leave a strange taste in your mouth for a few minutes. You might also feel that you need to urinate, but this sensation won’t last long.
  • During the scan, you will lie on a table that moves in and out of the CT scanner, which is large and round like a doughnut. Your chest, abdomen and pelvis will be scanned to check if the cancer has spread to these areas. The scan takes 5–10 minutes and is painless.
The dye used in a CT scan usually contains iodine. If you have had an allergic reaction to iodine or dyes during a previous scan, let your medical team know beforehand. You should also tell them if you’re diabetic, have kidney disease or are pregnant.

MRI scan

An MRI (magnetic resonance imaging) scan uses a powerful magnet to build up cross-sectional pictures of the inside of your body. Only people with cancer in the rectum have an MRI; it is not commonly used for cancers higher in the bowel. An MRI may be used before surgery to stage rectal cancer or before radiation therapy.

  • Before the scan, let your doctor know if you have a pacemaker or any other metallic object in your body. The magnet can interfere with some pacemakers, but some newer pacemakers are MRI-compatible. As with a CT scan, a dye might be injected into a vein before the scan to help make the pictures clearer.
  • During the scan, you will lie on an examination table that slides into a large metal tube that is open at both ends. The noisy, narrow machine makes some people feel anxious or claustrophobic. If you think you may become distressed, mention it beforehand to your medical team. You may be given a medicine to help you relax and you will usually be offered headphones or earplugs.
  • The MRI scan may take between 30 and 90 minutes, depending on the size of the area being scanned and how many images are taken.

FDG-PET scan

Medicare does not currently cover the cost of an FDG-PET (fluorodeoxyglucose-positron emission tomography) scan for bowel cancer, but this scan can find disease at sites that may not be picked up on a CT scan. If this test is recommended, check with your doctor what you will have to pay.

  • Before an FDG-PET scan, you will be injected with a special modified sugar molecule (fluorodeoxyglucose or FDG). You will be asked to sit quietly for 30–90 minutes while the solution moves through your body.
  • Your body is then scanned for areas with high levels of FDG. Cancer cells absorb more of the FDG, so they will be highlighted when your body is scanned.
  • It will take several hours to prepare for and have the scan.
Read more about CT, MRI and PET scans

Bowel preparation

Before some diagnostic tests, you will have to clean out your bowel completely. This will help the doctor see inside the bowel clearly.

Cleaning out the bowel is called bowel preparation. The process varies for different people and between hospitals, so ask if there are any specific instructions for you. It’s important to follow the instructions so you don’t have to repeat the test.

Talk to your doctor if you have any concerns about the bowel preparation process, or if you experience any side effects.

  • Change diet − For a few days before the diagnostic test, you may be told to avoid high-fibre foods, such as vegetables, fruit, wholegrain pasta, brown rice, bran, cereals, nuts and seeds. Instead, choose low-fibre options, such as white bread, white rice, meat, fish, chicken, cheese, yoghurt, pumpkin and potato.
  • Take prescribed laxatives − You will be prescribed a strong laxative to take 12–18 hours before the test. This is taken by mouth in tablet or liquid form, and will cause you to have watery diarrhoea.
  • Drink clear fluids − Your doctor might advise you to drink only fluids, such as broth, water, black tea and coffee, and clear fruit juice without pulp for 12–24 hours before the test. This will help to prevent dehydration.
  • Ask if you need an enema − One common way to clear the bowel is using an enema. This involves inserting liquid directly into the rectum. The enema solution washes out the lower part of the bowel, and is passed into the toilet along with any faeces.

Video: Cancer and common diagnostic tests

Learn more about what cancer is, how it spreads, and what primary and secondary cancers are. You can also find out about the tests that are commonly used to diagnose cancer, including CT/CAT scans, PET scans & MRI scans.

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