A variety of tests are used to examine the intestinal lining and stool samples. During a colonoscopy or sigmoidoscopy, a thin tube with a camera is inserted into the rectum to allow the doctor to see the intestinal lining and collect biopsies for testing. Fecal occult blood tests are used to detect blood in the stool (which may not be visible to the naked eye). DNA stool tests detect changes in the genetic material of intestinal cells, which can also be a sign of CRC. If a patient is diagnosed with CRC, other tests like x-rays and CAT scans are performed to determine whether the cancer may have spread to other areas.[1]