How is bowel cancer diagnosed?

Bowel cancer can be diagnosed with a number of different tests, which include a physical examination, blood tests, various procedures to inspect the bowel, and x-ray techniques.

What are the symptoms of bowel cancer?

Common signs and symptoms of bowel cancer may include:

• blood in your bowel motions (this may look like red blood or black bowel motions)
• a change in bowel habits
• diarrhoea, constipation, or feeling that your bowel doesn't empty completely 
• bowel motions that are narrower than usual
• general abdominal discomfort (frequent gas pains, bloating or cramps) that can be confused with indigestion
• unexplained weight loss
• tiredness
• anaemia.

As these symptoms are often caused by other conditions, it is important to check with a doctor without delay.

When you are diagnosed with bowel cancer, you may be concerned about your family’s risk of bowel cancer. While your family may not be at increased risk, you may wish to discuss with them the importance of reporting symptoms to their doctor early.

Diagnostic tests

You may have some or all of the following tests and procedures to check for bowel cancer.

Rectal and abdominal examination

During this examination the doctor inserts a gloved finger into the rectum to find any lumps, swelling or bleeding. The doctor will also gently feel the surface of the abdomen to check for anything abnormal.

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 the blood. It is sometimes raised in people with bowel cancer. However, it is not a reliable test to diagnose bowel cancer.

A test for blood in the bowel motions

Testing for blood in a sample of faeces can be carried out in a laboratory using an immunochemical faecal occult blood test (FOBT). This can detect blood not visible to the eye.

Barium enema

A radiologist puts a mixture containing barium into the rectum, and then takes x-rays. The barium shows up on the x-rays and gives a clear picture of the bowel. After the test, the mixture is passed out in the bowel motions.

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. CT scans are taken of your abdomen. If abnormalities are found, then this would usually lead onto a colonoscopy.

Sigmoidoscopy

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

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. A sedative may be given before 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'.

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.

Related topics

Also see Bowel cancer treatment and Bowel cancer

 What is cancer?,  What does that term mean? See Cancer glossary

Original material provided by the Cancer Society, 2009. Reviewed and edited by everybody, July 2010.