Effective & Trusted Medications Guide

Definition and description

Rectal bleeding (known medically as hematochezia) refers to passage of bright red blood from the anus, often mixed with stool and/or blood clots. (It is called rectal bleeding because the rectum lies immediately above the anus. Although the bleeding indeed may be coming from the rectum, as discussed later, it also may be coming from other parts of the gastrointestinal tract.) The severity of rectal bleeding (i.e., the quantity of blood loss) varies widely. Most episodes of rectal bleeding are mild and stop on their own. Many patients report only passing a few drops of fresh blood that turns the toilet water pink or seeing spots of blood on the tissue paper. Others may report brief passage of a spoonful or two of blood. Generally, mild rectal bleeding can be evaluated and treated in the doctor’s office without hospitalization or the need for urgent diagnosis and treatment.

Rectal bleeding also may be moderate or severe. Patients with moderate bleeding will repeatedly pass larger quantities of bright or dark red blood often mixed with blood clots. Patients with severe bleeding may pass several bowel movements or a single bowel movement containing a large amount of blood. Moderate or severe rectal bleeding can quickly deplete a patient’s body of blood, leading to symptoms of weakness, dizziness, near-fainting or fainting, and signs of low blood pressure or orthostatic hypotension (a drop in blood pressure when going from the sitting or lying position to the standing position). Rarely, the bleeding may be so severe as to cause shock from the loss of blood. Moderate or severe rectal bleeding usually is evaluated and treated in the hospital. Patients with signs and symptoms of a reduced volume of blood often require emergency hospitalization, and transfusion of blood.

Origin of rectal bleeding (where the blood comes from)

Most rectal bleeding comes from the colon, rectum, or anus. The colon is the part of the gastrointestinal tract through which food passes after it has been digested in the small intestine. The colon is primarily responsible for removing water from the undigested food and storing it until it is eliminated from the body as stool. The rectum is the last 15 cm of the colon. The anus (anal canal) is the opening through which stool passes when it is being eliminated from the body. Together, the colon, rectum, and anus form a long (several feet in length), muscular tube that also is known as the large intestine, large bowel, or the lower gastrointestinal tract. (The esophagus, stomach, duodenum, and small intestine are referred to as the upper gastrointestinal tract.)

The colon can be divided further into three regions; the right colon, the transverse colon, and the left colon. The right colon, also known as the ascending colon, is the part of the colon into which undigested food from the small intestine is first deposited. It is furthest from the rectum and anus. The transverse colon forms a bridge between the right and the left colon. The left colon is made up of the descending colon and the sigmoid colon. The sigmoid colon connects the descending colon to the rectum.

The color of the blood during rectal bleeding often depends on the location of the bleeding in the gastrointestinal tract. Generally, the closer the bleeding site is to the anus, the blood will be a brighter red. Thus, bleeding from the anus, rectum, and the sigmoid colon tend to be bright red, whereas bleeding from the transverse colon and the right colon tend to be dark red or maroon.

In some patients bleeding from the right colon can be black, “tarry” (sticky) and foul smelling. The black, smelly and tarry stool is called melena. Melena occurs when the blood is in the colon long enough for the bacteria in the colon to break it down into chemicals (hematin) that are black. Therefore, melena usually signifies bleeding is from the upper gastrointestinal tract (for example: bleeding from ulcers in the stomach or the duodenum or from the small intestine) because the blood usually is in the gastrointestinal tract for a longer period of time before it exits the body. Sometimes melena may occur with bleeding from the right colon. On the other hand, blood from the sigmoid colon and the rectum usually does not stay in the colon long enough for the bacteria to turn it black.

Rarely, massive bleeding from the right colon, from the small intestine, or from ulcers of the stomach or duodenal can cause rapid transit of the blood through the gastrointestinal tract and result in bright red rectal bleeding. In these situations, the blood is moving through the colon so rapidly that there is not enough time for the bacteria to turn the blood black. Sometimes, bleeding from the gastrointestinal tract (upper or lower) can be too slow to cause either rectal bleeding or melena. For example, slow bleeding from colon polyps or cancers can cause small amounts of blood to mix and be lost within the stool. Special tests (fecal occult blood tests) are needed to demonstrate the blood.