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.

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.