DIGESTIVE DISEASE CENTER | Gastroenterology home | Surgery home

Patient care — diagnostic tools, tests, procedures

Tests for colon cancer

Physical examination rarely shows abnormalities though an abdominal mass may be present. A rectal examination may reveal a mass in patients with rectal cancer, but not colon cancer.

A colonoscopy or sigmoidoscopy may reveal evidence of cancer. However only colonoscopy (NOT sigmoidoscopy) examines the entire colon.


A fecal occult blood test (FOBT) may detect small amounts of blood in the stool, a possible indicator of colon cancer. However, this test is often negative in patients with colon cancer.

Not all polyps bleed, and not all polyps bleed all the time. That is why a FOBT must be used with one of the other more invasive screening measures (e.g., colonoscopy or sigmoidoscopy).

Finally, a positive FOBT doesn't necessarily mean the person has cancer -- "false positives" can be caused by some medications and other factors.

A blood count may reveal evidence of anemia with low iron levels. CT scan may show an abdominal mass though this test is not very good at detecting colon cancer.

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