Bowel Cancer

Tests

Deciding which screening test to use and how often ultimately depends on a person's individual risk of bowel cancer. If a first-degree relative has had bowel cancer, for instance, screening should start 10 years prior to the age that relative was diagnosed to help identify possible pre-cancerous polyps.

The NHS Bowel Cancer Screening Programme now offers screening every two years to all men and women aged 60 to 69 in England using a guaiac based faecal occult blood test (gFOBT). The age range is currently being extended to 60 to 74. People within the age range are automatically sent an invitation, then their screening kit, so they can perform the test at home. After the first screening test, individuals are sent an invitation and screening kit every two years. The gFOBT does not diagnose bowel cancer, but the results will indicate whether an individual may need an examination of their bowel by colonoscopy.
For further information about the NHS Bowel Cancer Screening Programme see www.cancerscreening.nhs.uk/bowel/index.html. Separate screening programmes are offered in Wales, Scotland and Ireland.

There are four common screening tests for detecting bowel cancer:

• Faecal occult blood (FOB) test is a test for hidden blood in the stool.
• Sigmoidoscopy is an examination of the rectum and lower colon with a rigid or flexible lighted instrument. 
• Double barium contrast enema is a series of X-rays of the colon and rectum. The patient is given an enema with a white, chalky solution that outlines the colon and rectum on the X-rays.
• Colonoscopy is an examination of the rectum and entire colon with a lighted instrument. It may be the most useful, but it is also the most invasive.

There is also a newer test called CT colonography or virtual colonoscopy. Instead of having a colonoscope put inside the bowel, it may be possible to have an examination with pictures created by a computer. Air or carbon dioxide is pumped into the back passage to help open up the bowel. Two CT scans are performed; one when the patient is lying on their back and one lying on their front. A computer matches up the two scans and makes a 'virtual' scan of the inside of the bowel.

In addition to these, a doctor may perform a rectal examination to feel for a rectal mass with a gloved finger. Most bowel cancers, however, are beyond the reach of a finger and have no symptoms; hidden blood in the stool, detected as FOB, is often the first and only warning sign. There is also a potential future screening test still in development that looks for mutations in a specific gene (APC gene) that can be detected by analyzing the DNA from patients' stool samples.