Identification
Fresh blood in the stool is caused by bleeding in the digestive system. When the blood is fresh, it is generally caused by bleeding from the rectum or from the lower colon, because blood from higher in the gastrointestinal system (such as the esophagus or stomach) is usually clotted. When fresh blood occurs in the stool, it can range, colorwise, between bright red and a darker color, such as maroon. Fresh blood in the stool may be evident in the stool itself, or it may be seen on the toilet paper. In addition, small amounts of blood that are not visible to the naked eye may be detected by a special test, called a fecal occult blood test, which can be performed by a physician.
Cancer
One of the reasons why the appearance of fresh blood in the stool is so alarming is that it can indicate cancer. Two different kinds of cancer, anal and colon cancer, can lead to fresh blood in the stool. Cancer often causes bleeding because the cancerous cells grow out of control, leading to the lining of the anus or the colon (depending on the type of cancer) developing small ulcers or becoming unusually thin.
Another cancer-related cause of blood in the stool is the removal of small growths in the colon called polyps. It is believed that colon cancer develops from polyps. As a result, if a polyp is found in the colon, physicians will often remove it to prevent cancer from developing. As the colon recovers from the surgery, blood may appear in the stool.
Other Causes
There are many other causes for fecal blood aside from cancer. One of the most common is "out-pouchings" of the gastrointestinal tract. This occurs when the walls of the intestines become weak, and small portions of the underlying tissue begin to balloon out. Out-pouchings can cause hemorrhoids, diverticulosis and a genetic condition known as Menkel's diverticulum. These small out-pouchings cause the wall of the intestines to become thin and rupture easily.
Other causes of bleeding include rupture of the large intestine (due to constipation or trauma) or inflammation of the large intestine, which can be due to a parasite, bacteria or a problem with the immune system. Rectal bleeding can also be caused by a condition known as angiodysplasia, in which the blood vessels near the surface of the intestine swell and eventually rupture.
