What is rectal bleeding (hematochezia)?
Rectal bleeding (known medically as hematochezia) refers to the passage of red blood from the anus, often mixed with stools and/or blood clots. (It is called rectal bleeding because the rectum lies immediately above the anus, and 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 that is passed) 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 observing 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 (maroon-colored) blood often mixed with stools and/or 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 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 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 brighter red the blood will be. Thus, bleeding from the anus, rectum, and the sigmoid colon tends to be bright red, whereas bleeding from the transverse colon and the right colon tends to be dark red or maroon-colored.
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 bleeding is in the stomach where the blood is exposed to acid or is in the small intestine or colon for a long enough period of time for the intestinal bacteria to break it down into chemicals (hematin) that are black. Therefore, melena usually signifies that the 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 is exposed to stomach acid or is in the intestines for a longer period of time before it exits the body. Although it is possible for melena to occur with bleeding from the right colon, 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 duodenum 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) will be so minimal that it will not cause either rectal bleeding or melena. In such situations, blood can be found only by the use of special tests done on samples of stool. (See occult gastrointestinal bleeding)
Occult gastrointestinal bleeding
Rectal bleeding needs to be distinguished from another type of gastrointestinal bleeding, occult gastrointestinal bleeding. Occult gastrointestinal bleeding refers to a slow loss of blood into the upper or lower gastrointestinal tract that does not change the color of the stool or result in the presence of visible bright red blood. The blood is detected only by testing the stool for blood (fecal occult blood testing) in the laboratory. Occult bleeding has many of the same causes as rectal bleeding and may result in the same symptoms as rectal bleeding. For example, slow bleeding from ulcers, colon polyps, or cancers can cause small amounts of blood to mix and be lost within the stool. It is often associated with anemia that is due to loss of iron along with the blood (iron deficiency anemia).
What are the causes of rectal bleeding?
Many diseases and conditions can cause rectal bleeding. Common causes include:
- anal fissures,
- hemorrhoids,
- cancers and polyps of the rectum and colon,
- diverticulosis,
- abnormal blood vessels (angiodysplasia),
- ulcerative colitis,
- ulcerative proctitis,
- Crohn's colitis,
- infectious colitis,
- ischemic colitis, and
- Meckel's diverticula.
An anal fissure is a fairly common, painful condition in which the lining of the anal canal is torn. An anal fissure is caused by constipation or a forceful bowel movement, though a tight anal muscle also may be a contributing factor. Once the skin is torn, each subsequent bowel movement can be painful, and the pain often is severe. The amount of bleeding that occurs with an anal fissure is small and usually is noticed in the toilet bowl or on the toilet paper as bright red in color. The symptoms of an anal fissure are commonly mistaken for hemorrhoids, but hemorrhoids generally do not cause pain with bowel movements.
Hemorrhoids are masses or clumps ("cushions") of tissue within the anal canal that contain blood vessels. Although most people think hemorrhoids are abnormal, they are present in everyone. It is only when the hemorrhoidal cushions enlarge that hemorrhoids can cause problems (such as bleeding or anal discomfort) and be considered abnormal or a disease. Like anal fissures, bleeding from hemorrhoids is usually mild and does not cause anemia or low blood pressure. Rarely, a person may develop an iron deficiency anemia as a result of repeated hemorrhoidal bleeding over several months to years.
