There are two main types of stool tests to choose from. The first, a fecal occult blood test (FOBT), detects the presence of blood in your feces. The second, a stool DNA test, detects the presence of genetic material from polyps and cancerous tumors.
FOBT Stool Tests
FOBTs use a chemical reaction to check for the presence of blood in your stool. They may be performed in a doctor's office or at home. Guaiac FOBTs (gFOBTs) are the oldest type of stool test; they're the least accurate and the cheapest to buy over-the-counter.
Immunochemical FOBTs (iFOBTs) are a newer and more sensitive option for detecting blood in stool, but they're also more expensive. For example, Colon Health Check is an iFOBT and costs about $35. The iFOBT stool test detects the presence of hemoglobin, a protein found in blood.
Stool DNA Tests
The American Cancer Society (ACS) added stool DNA (sDNA) tests to its list of colon cancer screening options in March 2008. Rather than looking for hidden blood, sDNA tests look for traces of DNA (genetic material) shed by polyps and/or colorectal tumors. This is the most sensitive and expensive (about $80) stool test currently available.
It's important to note that stool testing is only an effective colon cancer screening option when used in combination with other methods. If your stool test comes back positive, the next step is to make an appointment with your doctor, who will probably order a colonoscopy or similar test.
Source: Can Colorectal Polyps and Cancer Be Found Early? American Cancer Society 5 Mar. 2008. Accessed 2 Nov. 2008 [http://www.cancer.org/docroot/CRI/content/CRI_2_4_3X_Can_colon_and_rectum_cancer_be_found_early.asp]