Bowel cancer

Diagnosing bowel cancer

On this page:

General tests | Bowel screeningTests to find cancer in the bowel | Bowel preparationFurther tests | Staging bowel cancer | Prognosis | Key points about diagnosing bowel cancer 


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.

The tests you have to diagnose bowel cancer depend on your specific situation. They may include general tests to check your overall health and body function, tests to find cancer, and 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. 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.

Cancer care pathways

For an overview of what to expect during all stages of your cancer care, from diagnosis to treatment and beyond, read or download the Guide to Best Cancer Care  for bowel cancer. This resource is also available in Arabic, Chinese, Greek, Hindi, Italian, Tagalog and Vietnamese – see details on the site.

General tests

Physical examination

Your doctor will examine your body, feeling your abdomen for any swelling. To check for problems in the rectum and anus, your doctor will insert a gloved, lubricated 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 anus 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 poo. 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.

Immunochemical faecal occult blood test (iFOBT)

Depending on your symptoms, you may have an iFOBT, which looks for tiny amounts of blood in your faeces. This test is generally not recommended for people who are bleeding from the rectum or have bowel symptoms (change in bowel habit, anaemia, unexplained weight loss, abdominal pain) as these people are usually referred for a colonoscopy straightaway.

The iFOBT involves taking a sample of your stools at home. The stool sample is examined for microscopic traces of blood, which may be a sign of polyps, cancer or another bowel condition. An iFOBT does not diagnose cancer, but if it finds blood, your doctor will recommend you have a colonoscopy as soon as possible, but no later than 30 days after getting the result.

“I had very light blood streaks on toilet paper when wiping my bottom. After two weeks of this, I went to my doctor thinking it was haemorrhoids but he sent me for a colonoscopy.” - Richard 

Screening test for bowel cancer

Screening is the process of looking for cancer or abnormalities that could lead to cancer in people who do not have any symptoms. It is particularly important for bowel cancer, which often has no symptoms in its early stages.

Through the National Bowel Cancer Screening Program, people aged 50–74 are automatically sent a free iFOBT kit every two years. A test kit can also be purchased from some pharmacies. The test is conducted from home and then sent back. You don’t need to change what you eat or stop your medication. If the screening test is positive, further tests are needed. It is very important that you do the iFOBT as it can find precancerous polyps and early cancers in the bowel. Removing polyps reduces the risk of developing bowel cancer, and finding bowel cancer early can greatly improve the chance of surviving the disease.

If you have questions about how to do the test, call 1800 930 998 or visit the Department of Health website. If you are an Indigenous Australian, visit Indigenous Bowel Screen online. If the screening test is negative, you’ll receive another test in two years, up to the age of 74. If you develop symptoms between screening tests, let your doctor know. 

Screening for people with a higher risk

The National Bowel Cancer Screening Program is for people without symptoms of bowel cancer. If you have:

  • symptoms of bowel cancer – talk to your doctor about having a colonoscopy or other tests
  • another bowel condition, such as chronic inflammatory bowel disease – talk to your doctor about appropriate surveillance
  • a strong family history or a genetic condition linked to bowel cancer – talk to your doctor about when you need to start iFOBTs or screening colonoscopies. 

Tests to find cancer in the bowel

The main test used to look for bowel cancer is a colonoscopy. Other tests that are sometimes used to diagnose bowel cancer include CT colonography and sigmoidoscopy.

Colonoscopy and biopsy

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.

Most colonoscopies are done as an outpatient procedure at a hospital. Before a colonoscopy, you will have a bowel preparation to clean your bowel. On the day of the procedure, you will usually be given a sedative or light 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 colonoscope (a flexible tube with a camera on the end) into your anus and up into your rectum and colon. Carbon dioxide or air will be passed into the colon to make it easier for the doctor to see the bowel.

If the doctor sees any abnormal or suspicious-looking areas, they will remove a tiny sample of the tissue for examination. This is known as a biopsy. During the colonoscopy, most polyps can be completely removed (a polypectomy). A pathologist will examine the tissue under a microscope to check for signs of disease and may look for specific genetic changes (see Molecular testing).

A colonoscopy usually lasts 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 flatulence, bloating and wind pain. 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

CT colonography

This uses a CT scanner to create images of the colon and rectum and display them on a screen. It is also called virtual colonoscopy. It may be used if the colonoscopy was unable to show all of the colon or when a colonoscopy is not safe.

A CT colonography is not often used because it is not as accurate as a colonoscopy and exposes you to radiation. Your doctor also may not be able to see small abnormalities and cannot take tissue samples. This test is covered by Medicare only in some limited circumstances.

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 a light bowel clean-out, usually with an enema. 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 your doctor can take tissue samples (biopsy).

Bowel preparation

Before some tests, you will have to clean out your bowel completely to make sure the doctor can see the bowel clearly. This is called bowel preparation or washout. The process can vary, so ask your doctor what you need to do. It’s important to follow the instructions so you don’t have to repeat the test.

information on preparing your bowel for tests

Further tests

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

CEA blood test

Your blood may be tested for a protein produced by some cancer cells. This is called a tumour marker. The most common tumour marker for bowel cancer is called carcinoembryonic antigen (CEA).

If the results of the blood test 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 the level of CEA. If your CEA level is high, it will be retested after treatment to see if it has returned to normal. Not all bowel cancers have a raised CEA.

CT scan

A CT (computerised tomography) scan uses x-ray beams to create detailed, cross-sectional pictures of the inside of your body. 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.

MRI scan

An MRI (magnetic resonance imaging) scan uses a powerful magnet and radio waves to create detailed, cross-sectional pictures of the inside of your body. An MRI is recommended to more accurately determine the position and extent of rectal cancer. An MRI may also be used to scan the liver if your doctor suspects the cancer has spread to the liver. Usually only people with cancer in the rectum have an MRI; it is not commonly used for cancers higher in the bowel.

A dye might be injected into a vein before the scan to help make the pictures clearer. During the scan, you will lie on a treatment 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 could 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.

Before having scans, tell the doctor if you have any allergies or have had a reaction to dyes during previous scans. You should also let them know if you are diabetic, have kidney disease or are pregnant.

PET-CT scan

A positron emission tomography (PET) scan combined with a CT scan is a specialised imaging test. The two scans provide more detailed and accurate information about the cancer. A PET-CT scan is most commonly used after surgery to help find out where the cancer has spread to in the body or if the cancer has come back after treatment.

Before the scan, you will be injected with a glucose solution containing a small amount of radioactive material. Cancer cells show up brighter on the scan because they take up more glucose solution than the normal cells do. You will be asked to sit quietly for 30–90 minutes as the glucose spreads through your body, then you will be scanned. The scan itself will take around 30 minutes. Let your doctor know if you are claustrophobic as the scanner is a confined space.

Medicare only covers the cost of PET-CT scans for bowel cancer in limited circumstances. If this test is recommended, check with your doctor what you will have to pay.

Molecular testing

If you are diagnosed with advanced bowel cancer, your doctor may order extra tests on the biopsy sample to look for particular features that can cause the cancer cells to behave differently. These tests may look for mutations in the RAS and BRAF genes or features in the cancer cells suggesting that further genetic testing is required. Knowing whether the tumour has one of these features may help your treatment team determine suitable treatment options. See Systemic treatment for more details.

Staging bowel cancer

The tests described above help show whether you have bowel cancer and whether it has spread from the original site to other parts of the body. Working out how far the cancer has spread is called staging and it helps your health care team decide the best treatment for you.

In Australia, there are two main systems used for staging bowel cancer:

  • the Australian Clinico-Pathological Staging (ACPS) system
  • the TNM staging system – TNM stands for tumour–nodes– metastasis. Each letter is assigned a number to show how advanced the cancer is.

Your doctor will combine the results of your early tests, as well as the tests on the cancer tissue and lymph nodes removed during surgery, to work out the overall stage of the cancer:

  • stage I (ACPS A) – tumours are found only in the lining of the bowel (early or limited disease)
  • stage II (ACPS B) – tumours have spread deeper into the layers of the bowel walls (locally advanced disease)
  • stage III (ACPS C) – cancer has spread to nearby lymph nodes (locally advanced disease)
  • stage IV (ACPS D) – tumours have spread beyond the bowel to other parts of the body, such as the liver or lungs, or to distant lymph nodes (advanced or metastatic disease).

In general, earlier stages have better outcomes. Almost 50% of bowel cancers in Australia are diagnosed at stages I and II. If you are finding it hard to understand staging, ask someone in your medical team to explain it in a way that makes sense to you.


Prognosis means the expected outcome of a disease. You may wish to discuss your prognosis and treatment options with your doctor, but it is not possible for any doctor to predict the exact course of the disease. Instead, your doctor can give you an idea about the general prognosis for people with the same type and stage of cancer.

Generally, the earlier that bowel cancer is diagnosed, the better the chances of successful treatment. If cancer is found after it has spread beyond the bowel to other parts of the body, it may still respond well to treatment and can often be kept under control.

Test results, the type of cancer, the rate and depth of tumour growth, the likelihood of response to treatment, and factors such as your age, level of fitness and medical history are important in assessing your prognosis. These details will also help your doctor advise you on the best treatment options.

To help people with bowel cancer receive the best care possible, we have developed an optimal cancer care pathway. View the guide to make sure you get the best care and support at each stage.

Key points about diagnosing bowel cancer

General tests

General tests to investigate abnormal symptoms include a digital rectal examination (DRE), blood tests, and an immunochemical faecal occult blood test (iFOBT) to look for traces of blood in the stools.

Main test

  • A colonoscopy looks for polyps and cancer in the entire large bowel
  • Before a colonoscopy you will have a bowel preparation to clean out the bowel so the doctor can see inside more clearly
  • If the doctor sees a suspicious-looking area, they will take a tissue sample (biopsy).

Other tests

Other tests can give more information about the cancer to help guide treatment. These tests may include:

  • a blood test to check for a protein called carcinoembryonic antigen (CEA), which is produced by some cancer cells
  • imaging scans (CT, MRI or PET-CT) to show the location of the cancer and whether it has spread
  • molecular testing for gene mutations in the cancer cells.

Staging and prognosis

The stage shows how far the cancer has spread through the body. Early bowel cancer is stage I. Locally advanced bowel cancer is stages II and III. Advanced bowel cancer is stage IV. In general, earlier stages have better outcomes.


Expert content reviewers:

A/Prof David A Clark, Colorectal Surgeon, Royal Brisbane and Women’s Hospital, and The University of Queensland, QLD, and The University of Sydney, NSW; A/Prof Siddhartha Baxi, Radiation Oncologist and Medical Director, GenesisCare Gold Coast, QLD; Dr Hooi Ee, Specialist Gastroenterologist and Head, Department of Gastroenterology, Sir Charles Gairdner Hospital, WA; Annie Harvey, Consumer; A/Prof Louise Nott, Medical Oncologist, Icon Cancer Centre, Hobart, TAS; Caley Schnaid, Accredited Practising Dietitian, GenesisCare, St Leonards and Frenchs Forest, NSW; Chris Sibthorpe, 13 11 20 Consultant, Cancer Council Queensland; Dr Alina Stoita, Gastroenterologist and Hepatologist, St Vincent’s Hospital Sydney, NSW; Catherine Trevaskis, Gastrointestinal Cancer Specialist Nurse, Canberra Hospital, ACT; Richard Vallance, Consumer.

Page last updated:

The information on this webpage was adapted from Understanding Bowel Cancer - A guide for people with cancer, their families and friends (January 2021). This webpage was last updated in March 2021. 

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