Diagnosing bowel cancer

Thursday 31 January, 2013

 On this page: Cancer screening tests | General tests | Tests to find cancer | Bowel preparation | Further tests | Staging bowel cancer | Prognosis | Health Professionals | Reviewers  

Your GP will examine you and 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).

Some tests may be repeated during or after treatment to check how well the treatment is working.

Waiting for the test results can be a stressful time. It may help to talk to a friend or family member, a healthcare professional, or call Cancer Council on 13 11 20.

Cancer screening tests

Bowel cancer is a common cancer, so you may have a screening test. Screening is the process of looking for cancer in people who don't have any symptoms.

Faecal occult blood test

This screening test looks for blood in your stools (faeces), which may be a sign of cancer or another bowel condition. The faecal occult blood test (FOBT) can find traces of blood in the faeces that are invisible to the naked eye but can be seen with a microscope.

An FOBT can be done at home, using a kit that costs $30 to $40. You'll usually need to take samples from two separate bowel motions and send them in the envelope provided to a laboratory. The samples are examined under a microscope.

If the test is positive (you have blood in your stool), contact your doctor, who'll be able to advise you about the next steps. Your doctor will check for haemorrhoids and other non-cancerous conditions, and do further tests to check for bowel cancer.

The FOBT is recommended to people aged 50 and older, every two years, because ageing is one of the risk factors for bowel cancer.

National Bowel Cancer Screening program

The Australian Government offers free FOBT kits to people turning 50, 55, 60, 65, 70 or 74. By 2020 it will be available free to all Australians aged 50–74.

An FOBT doesn't diagnose bowel cancer. It's a simple, non-invasive method of showing whether further tests such as a colonoscopy (see below) may be required.

Research shows that 90% of bowel cancers are curable if found early.

To be eligible for a free test, you need to have a Medicare card or a Veterans Affairs card. You'll automatically be sent an invitation to participate within six months of your birthday. You don't have to participate in the screening program but it's highly recommended.

For more information phone 1800 738 365 (free call from fixed phone line).

General tests

Physical examination

Your doctor will examine your body, feeling your abdomen for any swelling. To check for problems in the anus and rectum, your doctor will insert a gloved finger into your anus to feel inside for any lumps or swelling. This is called a digital rectal examination (DRE), and it helps the doctor detect problems in the lowest part of the bowel.

The DRE may be uncomfortable, but it shouldn't be painful. It might make you feel like you're going to open your bowels, but it's very unlikely that this will happen. Because the rectum is a muscle, it can help to try to relax during the test.

Sometimes the doctor will insert a small, rigid telescope (sigmoidoscope or proctoscope) into the anus to see the lining of the lower part of the bowel. You don't need to empty your bowel or have an anaesthetic for this test.

Blood test

You may have a blood test to assess your general health and to look for signs that you are losing blood in your stools. Some doctors also measure the levels of carcinoembryonic antigen (CEA), which is a protein produced by some cancer cells. If your blood tests show that you have a high CEA level, your doctor may organise more tests. This is because other conditions, such as smoking or pregnancy, may also increase CEA levels. The blood test may also measure chemicals that are found or made in your liver, and check your red blood cell count. Low red blood cell levels (anaemia) is common in people with bowel cancer, but may also be caused by other conditions.

Tests to find cancer

Flexible sigmoidoscopy

This test allows the doctor to see the rectum and the left side of the lower part of the colon. To have a flexible sigmoidoscopy, you'll need to have an empty bowel.

Before the test, your doctor may give you a light anaesthetic. You'll lie on your left side on an examination table, and the instrument will be gently inserted into your anus and through the bowel.

The sigmoidoscope blows air into the bowel. This inflates the bowel slightly and allows the doctor to see the bowel wall mor clearly. Any unusual areas can be seen with the camera and light at the end of the tube. The doctor can also use the sigmoidoscope to remove a piece of tissue for examination. This is called a biopsy.

A sigmoidoscopy takes about 10 to 20 minutes. Though it may feel uncomfortable, it shouldn't be painful. Cramping and pressure in your lower abdomen will ease when the air leaves your colon after the test is over (by passing gas). 


A colonoscopy examines the whole length of the large bowel. This is the best, most accurate test to examine the large bowel for cancer in most people.

  • Before a colonoscopy, you'll have a bowel preparation to clean your bowel. On the day of the procedure, you'll 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 examination.
  • The doctor will insert a flexible tube with a camera on the end, called an endoscope, into your anus and up into your rectum and colon.
  • Air will be pumped into your colon, and your doctor will look for abnormal tissue (such as polyps), which will be removed for further examination (biopsy).

The main side effect of a colonoscopy is temporary flatulence and wind pain, which is due to air pumped into the large 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. Overall, the test is safe and the benefits far outweigh the risks for most people.

A colonoscopy usually takes about 20 to 30 minutes. You'll need to have someone take you home after the colonoscopy, as you may feel drowsy or weak.

Screening colonoscopies

If one of your family members has had bowel cancer at a young age (less than 55 years), or more than one member of your extended family has had bowel cancer, your doctor may recommend that other family members have a screening colonoscopy as a precaution.

Screening colonoscopies are recommended at 50 years of age, or 10 years before the age of the youngest person with cancer, whichever comes first. 

Virtual colonoscopy

A virtual colonoscopy uses a CT or MRI scanner to create images of the colon and rectum and display them on a screen instead of putting an endoscope into your bowel.

Your bowel needs to be empty for the colonoscopy, so you'll have a bowel preparation (see below). You'll probably lie on your back or stomach and a thin tube will be inserted into your rectum to pump air into your colon. This may feel uncomfortable. After your colon is inflated, you'll be moved into the scanner.

The scanner will create 3D images of your colon while you hold your breath for short intervals.

Although a virtual colonoscopy is less invasive than a colonoscopy and your bowel can be seen in detail, your doctor may not be able to see small abnormalities or take tissue samples. If the doctor suspects any abnormalities, or if the scan results are unclear, you'll also be advised to have a standard colonoscopy. 

Barium enema

A barium enema is a type of bowel x-ray procedure. Barium is a white contrast liquid that shows up on x-rays. Before having this procedure, you will have a bowel preparation. During the procedure, you'll lie on an x-ray table while a barium-filled tube is inserted into your rectum and released into your colon. The doctor may also pump air into your colon to force the enema fluid into creases in the bowel wall.

The barium will show up any lumps or swellings, and x-rays of your inflated colon will then be taken. This 30-minute test can be uncomfortable, but it's not painful.

For a couple of days afterwards, your stools may be white. This is the barium being removed from the body. It can also cause constipation, however taking a mild laxative for a couple of days may help.

If an abnormal area is found, you'll probably need to have a colonoscopy or other type of test.

Bowel preparation

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

The cleaning process varies between hospitals and for different people, so ask if there are any instructions for you to follow. It's important to follow the instructions so you don't have to repeat the test.

Consider using soft toilet paper, wet wipes or barrier cream so your skin doesn't get irritated during preparation. Preparation may involve:

  • Having an enema: One common way to clear the bowel is using an enema. This is liquid that is inserted directly into the rectum. The enema solution washes out the bowel, and is usually passed into the toilet along with any faeces.
  • Taking laxatives: Another type of bowel preparation is an oral laxative (in tablet or liquid form), which will cause you to have watery diarrhoea.
  • Making diet changes: 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.
  • Drinking 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. It's important to drink plenty of fluid during the preparation to prevent dehydration.

Talk to your doctor if you're concerned about anything during the bowel preparation.

Further tests

If the tests described above show you have bowel cancer, you'll have one or more scans to see if the cancer has spread to other parts of your body. A scan is painless and is usually done as an outpatient. Most people are able to go home as soon as the test is over. 

CT scan

A CT (computerised tomography) scan uses x-ray beams to create a detailed picture of the inside of the body.

Before the scan, dye is injected into a vein to make the pictures clearer. This may make you feel hot all over for a few minutes and leave a strange taste in your mouth.

The CT scanner is large and round like a doughnut. You'll lie on a table that moves in and out of the scanner. It takes about 30 minutes to set up the machine, however, the scan itself takes 5 to 10 minutes. 

The dye used for a CT or MRI scan is called a contrast solution and may contain iodine. If you're allergic to iodine, shellfish, fish or dyes, let the person performing the scan know in advance. 

MRI scan

An MRI (magnetic resonance imaging) scan uses radio waves and magnetism to create cross-sectional pictures of the body. Dye may be injected into a vein before the scan to help make the pictures clearer. You'll lie on a table that slides into a metal cylinder that's open at both ends. Some people feel anxious lying in the narrow metal cylinder. You may be given a mild sedative to help you relax.

Before arranging the test, your doctor will ask you questions about your medical history to check you can have the test. People who have a pacemaker or other metallic objects in their body can't have an MRI due to the effect of the magnet.

PET scan

During a PET (positron emission tomography) scan you'll be injected with a small amount of radioactive glucose solution. It takes 30 to 90 minutes for the solution to circulate around your body. You'll be asked to sit quietly during this time.

Your body is then scanned for high levels of radioactive glucose. Cancer cells show up brighter on the scan because they're more active and take up more of the glucose solution than normal cells.

Though it may take several hours to prepare for and have a PET scan, it's usually done on an outpatient basis.


An ultrasound is a test that uses soundwaves to build up a picture of your body. A device (transducer or probe) is placed on or in your body. This sends out soundwaves that echo when they meet something dense, like a tumour, and images are projected onto a computer screen. There are two types of ultrasounds depending on the type of cancer you have:

  • Abdominal ultrasound: This may be done to see whether bowel cancer has spread to the liver. A gel is spread over your abdomen to conduct the soundwaves and the transducer is passed over the abdominal area to create the image. The test takes 15 to 20 minutes. 
  • Endorectal ultrasound (ERUS): A probe is inserted through the anus into your rectum. This can be uncomfortable, and there may be some light bleeding from the rectum. However, it takes about 10 minutes.

An ERUS is usually done if other tests show there's cancer in the rectum or anus. It helps your doctor determine the size of the cancer and if it has spread into the bowel wall. It may also help the doctor plan surgery or decide if other treatments are needed. 

A chest x-ray may be taken to check if the cancer has spread to the lungs or lymph nodes in your chest.

Reviewed by: Karen Barclay, Colorectal Surgeon, The Northern Hospital, Lecturer in Surgery, University of Melbourne, VIC; Carole Arbuckle, Cancer Nurse, Cancer Council VIC; Karen Bowers, Eat it to Beat it Strategy Project Officer, Cancer Council NSW; Darrell Bowyer, Consumer; Rebecca Foot-Connolly, Stomal Therapy Nurse, The Alfred Hospital, VIC; Bernadette Hadfield, Stomal Therapy Nurse, The Alfred Hospital, VIC; Melissa Heagney, Media and Communications Advisor, Cancer Prevention Unit, Cancer Council VIC; Dorothy King, Consumer; and Loreto Pinnuck, Stomal Therapist, Wound Consultant, Paediatric Continence Specialist, Monash Medical Centre, VIC. Thanks to Paul Zuiderwyk for sharing his story. 
Updated: 31 Jan, 2013