A procedure called a fecal occult blood test (FOBT) detects invisible amounts of blood in the feces, a possible sign of several disorders, including colon cancer. The test is painless and can be done at home or in the doctor's office along with a rectal exam. With an application stick, a dab of a stool specimen is smeared on a chemically treated card, which is tested in a laboratory for evidence of blood. If blood is confirmed in the stool, more elaborate tests may be performed to find the source of the bleeding. Some other options include sigmoidoscopy and colonoscopy. The former exam uses a lighted instrument called a sigmoidoscope to find precancerous or cancerous growths in the rectum and lower colon. The latter exam uses a lighted instrument called a colonoscope to find precancerous or cancerous growths throughout the colon, including the upper part. source :Comprehensive Cancer Information - National Cancer Institute
