How is bowel cancer diagnosed?


You will probably see many doctors, nurses and health professionals, who will work together as a multidisciplinary team to diagnose and treat you. It may be helpful to keep together documents about your appointments, information, letters and useful contacts. This will make it easier for you to know who to call and which doctors you have seen.

For most people, their bowel cancer is found after having symptoms. For others it may be discovered following a medical check-up. If you have symptoms, your general practitioner may arrange a test that involves having the inside of your bowel looked at. This could be with a short tube (sigmoidoscope) or a long tube with a small camera on the end (colonoscope). Sometimes a CT scan (computerised tomography scan) can be used to look at the inside of the bowel (CT colonography).

It can be a worrying time waiting for results, especially if you need several tests. If these tests do not rule out cancer but concern persists, it is usual to be referred to a bowel specialist. They will arrange further tests and advise you about treatment options. The purpose of these tests is to find out the type of bowel cancer you have and if the cancer has spread to other parts of your body. You may need to travel to another hospital for some tests.

Screening for bowel cancer

In New Zealand, a bowel cancer screening programme is being rolled out region by region for those without symptoms. 

The National Bowel Screening Programme is free for men and women aged 60 to 74 years who are eligible for publicly funded healthcare. It aims to save lives by finding bowel cancer at an early stage when it can often be successfully treated. 

For more information, talk to your doctor, call 0800 924 432, or visit the screening website: www.timetoscreen.nz/bowel-screening/


Abdominal examination

The doctor feels the surface of your abdomen to check for any lumps.

Rectal examination

The doctor inserts a gloved finger into your rectum to check for any lumps, swelling or bleeding.

The tests you may have

X-rays, CT scans or PET (positron emission tomography) scans and MRI (magnetic resonance imaging) scans are used to make images of the inside of your body to see if you have a lump and if it has spread. These can be done before or after surgery.

Blood count

A sample of your blood is taken to count the number of red cells in your blood (a low level [anaemia] can be a sign of bowel cancer).

Carcinoembryonic antigen (CEA)

CEA is a blood test that looks at a protein in your blood. The protein level is sometimes raised in people with bowel cancer; however, there are some conditions that are not cancer (for example, smoking) that can cause it to be raised. 

CEA on its own does not diagnose bowel cancer, but if you have been diagnosed with bowel cancer, it can be useful for tracking progress. 

A test for blood in the bowel motions (faecal occult blood)

This is most commonly used as a screening tool as part of a screening programme for bowel cancer. It is less helpful if you have abdominal symptoms. A normal faecal occult blood test does not exclude bowel cancer.

Barium enema

This is an older test using barium and X-rays to look at the lining of your bowel. There are now better tests than this available, and most doctors do not recommend this test anymore.


CT colonography (also known as virtual colonoscopy)

This X-ray technique is increasingly replacing barium enemas. The colon is emptied with a laxative. Air is then gently pumped into your bowel via your anus (the entry to your rectum). CT scans are taken of your abdomen. If abnormalities are found, this usually leads to a colonoscopy.


The doctor examines your rectum and the lower part of your bowel using a short tube (which is usually straight but may be flexible) called a sigmoidoscope. The doctor may also take a biopsy (a small sample of tissue).


Before your test you are given instructions on how to prepare your bowel for a colonoscopy. The doctor or nurse inspects the entire length of your large bowel by gently inserting a long, flexible tube with a video camera in it (called a colonoscope). This is passed through your anus and rectum into your colon (see the diagram below). You may be offered medication to help you relax during the colonoscopy.


Removing polyps at colonoscopy

If you have a pre-cancerous lesion, such as an adenomatous polyp of the colon or rectum, your surgeon or gastroenterologist may just remove the polyp from the bowel lining. A border of healthy tissue will also be removed. This is called a local resection.

Diagram showing a local resection of an early-stage bowel cancer


Bowel Cancer 2018 for website removal polyp

(Copyright: Cancer Research UK)

If there are any cancer cells within the polyp, your surgeon may decide you need a second, larger operation. This is to remove any cells that may have been left behind, and to make sure that the cancer is unlikely to come back.


CT scan (sometimes called a CAT scan)

CT scans use X-rays to take three-dimensional (3D) picturesof the inside of your body. CT scans are usually done at a hospital or radiology service, and can be used to find smaller cancers than those found by X-rays. CT scans can also show enlarged lymph nodes or may show cancer in other parts of your body.
You may be asked to not eat or drink for a few hours before the CT scan. A dye (iodine contrast) may be injected into your arm to make the scan pictures clear. For some scans you may be asked to drink a lot of water. This is so that the kidneys can cope easily with the dye. Before the scan, tell your medical team if you are allergic to iodine, fish or dyes, or if you have kidney problems. A CT scan may take 10 to 30 minutes. You lie flat on a bench, which moves you through the centre hole in the CT scanner, a machine shaped like a doughnut. 

MRI (magnetic resonance imaging)

This is a scan using magnetic fields and radio waves to build a picture of the organs inside your body.The MRI machine is similar to a CT scanner, but has a longer
central hole, more like a cylinder (tube). Scanning is very noisy. You will be offered earphones (with or without music) to reduce the sound. Some people feel claustrophobic
(closed in) when they are having a scan. If you think this may happen to you, let your doctor know when they book your appointment as they may be able to prescribe medication to help you relax before the scan.

PET (positron emission tomography) scan

PET scans are only available in a few New Zealand cities. A PET scan can be used to help stage bowel cancer (see page 26) and look for cancer that may have spread to other parts of your body. Most people do not need PET scans, but they can be helpful—particularly if other tests are inconclusive or if doctors are considering removing secondary cancer. 
Before the scan, a radioactive glucose (sugar) solution is injected into your arm. It takes 30 to 90 minutes for the body to absorb the radioactive solution. Then you have two types of scan. One scan looks for where in the body the radioactive glucose solution has built up. The other is a CT scan to match these areas to the different parts within your body. This combination of scans is sensitive and will find areas of the body affected by bowel cancer. If you are diabetic, it is important to have good diabetic control before this test. Talk to your doctor or nurse if your sugar levels are high.