Rectal Bleeding (Blood in the Stool) Causes & Treatment

Facts you should know about rectal bleeding

Picture of colon anatomy and sources of rectal bleeding

Rectal bleeding is the passage of blood through the anus. The bleeding may result in bright red blood in the stool as well as maroon-colored or black stool. The bleeding also may be occult (not visible with the human eye).
The common causes of rectal bleeding from the colon include anal fissure, hemorrhoids, diverticulosis, colon cancer and polyps, colonic polyp removal, angiodysplasias, colitis, proctitis, and Meckel's diverticula.
Rectal bleeding also may be seen with bleeding that is coming from higher in the intestinal tract, from the stomach, duodenum, small intestine, or Meckel's diverticulum.
Rectal bleeding may not be painful; however, other symptoms that may accompany rectal bleeding are diarrhea, and abdominal cramps due to the irritation caused by the blood in the stool.
Rectal bleeding is commonly evaluated and treated by gastroenterologists and colorectal or general surgeons.
The origin of rectal bleeding is determined by history and physical examination, anoscopy, flexible sigmoidoscopy, colonoscopy, radionuclide scans, visceral angiograms, upper gastrointestinal endoscopy, or capsule endoscopy of the small intestine, and blood tests.
Rectal bleeding is managed first by correcting any low blood volume and anemia if present with blood transfusions and then, determining the site and cause of the bleeding, stopping the bleeding, and preventing future rebleeding.
Rectal bleeding can be prevented if the cause of the bleeding can be found and definitively treated, for example, by removing the bleeding polyp or tumor. In addition, it may be appropriate to search for additional abnormalities, for example, polyps or angiodysplasias that have not yet bled but may do so in the future. This may require either gastrointestinal endoscopy or surgery.

Rectal Bleeding (Blood in Stool) Symptoms

Blood in the stool or rectal bleeding is a symptom of a disease or condition.

The color of blood in the stool can be:

bright red,
maroon,
yellow,
white,
green,
black and tarry, or
not visible to the naked eye (occult).

Causes of blood in stool range from harmless, annoying conditions of the gastrointestinal tract such as hemorrhoids
or anal fissures, to serious conditions such as cancer.

What does rectal bleeding (blood in stool) mean?

Rectal bleeding (known medically as hematochezia) refers to the passage of 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, but red blood in the stool may be coming from the rectum, as discussed later, but 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 observing a few drops of fresh blood that turns the toilet water pink or observing spots of blood on the tissue paper after they wipe. 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.

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 stool 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, 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.

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What are causes of blood in the stool (rectal bleeding)?

Color of blood in the stool

Blood in the stool primarily comes from the upper gastrointestinal tract (stomach and duodenum although occasionally the esophagus) or the lower gastrointestinal tract (colon, rectum, and anus). Although the small intestine also may be the source of blood in the stool, compared to the upper and lower parts of the gastrointestinal tract, the small intestine is infrequently the source. Most people think of blood in the stool as meaning that the stool contains red blood, but this is not always true. As discussed previously, the bloody stool may be maroon colored or black.

The colon is the part of the gastrointestinal tract through which undigested food passes after the digestible part of the food has been digested and absorbed in the small intestine. The colon is primarily responsible for removing water from the undigested food, and storing the undigested food until it is eliminated from the body as stool. The rectum is the last 15 cm (6 inches) of the colon. The anal canal, approximately an inch in length, connects the rectum with the anus opening through which stool passes when it is eliminated from the body. Together, the colon, rectum, anal canal, 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 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, anal canal, 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 in the stool often depends primarily 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. With bleeding from the upper GI tract and depending on how long the blood remains in the stomach and small intestine, the color in the stool will change from bright red, to maroon, to black. Blood in the stool that is red or maroon is most commonly is referred to as rectal bleeding.

Bleeding that occurs from the stomach and duodenum frequently is black, "tarry" (sticky), and foul smelling. The black, smelly and tarry stool is called melena. Melena mostly occurs when the bleeding is in the stomach where the blood is exposed to acid or is in the small intestine for a prolonged amount of time; however, melena also may occur with bleeding from the colon if the transit of the blood through the colon is slow, and there is enough time for the intestinal bacteria to break the blood down into chemicals (hematin) that are black.

Blood from the sigmoid colon, rectum and anus 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 darker or black.

Occult gastrointestinal bleeding

Another "type" of blood in the stool is occult blood. 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. Blood in the stool is detected only by testing the stool for blood (fecal occult blood testing) in the laboratory. Occult blood in the stool has many of the same causes as rectal bleeding, and may be associated with the same symptoms as more active 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. Chronic occult bleeding often is associated with anemia due to the loss of iron along with the blood (iron deficiency anemia).

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What diseases and conditions can cause blood in the stool (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 in the lining of the intestines (angiodysplasia)
Ulcerative colitis
Ulcerative proctitis
Crohn's colitis
Infectious colitis
Ischemic colitis
Meckel's diverticula

As discussed previously, it also is possible for "rectal bleeding" to be coming from the stomach and duodenum, primarily from ulcers, cancers, and angiodysplasias.

Anal fissures

An anal fissure is a fairly common, painful condition in which the lining of the anal canal is torn. An anal fissure usually is caused by physical trauma due to constipation or a forceful bowel movement through a tight anal muscle or physical trauma also may be contributing factors. 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.

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Hemorrhoids

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 become susceptible to trauma from passing stool and cause problems (such as bleeding or anal discomfort) and are considered abnormal or a disease. Like anal fissures, bleeding from hemorrhoids usually is mild and does not cause anemia or low blood pressure. Rarely, a person may develop iron deficiency anemia as a result of repeated hemorrhoidal bleeding over several months to years, especially if the dietary intake of iron is low.

Picture of the formation of hemorrhoids

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Colon cancer and polyps

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Tumors of the colon and rectum are growths (masses) arising from the wall of the large intestine. Benign tumors of the large intestine usually are called polyps because of their shape. Malignant tumors of the large intestine are cancers, and most are believed to have developed from polyps. Bleeding from colon polyps and cancers tends to be mild (the amount of blood loss is small), intermittent, and usually does not cause low blood pressure or shock.

Cancers and polyps of the colon and rectum can cause bright red rectal bleeding, maroon colored stools, and sometimes melena. The colon cancers and polyps located near the rectum and the sigmoid colon are more likely to cause mild intermittent bright red rectal bleeding, while colon cancers located in the right colon are more likely to cause occult bleeding that over time can lead to moderate or severe iron deficiency anemia.

Picture of the colon with colon cancer and colon polyps

Diverticulitis

Diverticulosis is a condition in which the colon contains outpouchings (little sacks). Diverticula are present in a majority of people who reach the age of 50-60 years. The cause of colonic diverticula is not entirely known, but may be contributed by years of high pressure within the colon or a weakness in the wall of the colon. Diverticula are permanent, and no diet will cause them to disappear. The only way to rid a person of diverticula is to surgically remove the part of the colon that contains the diverticula. A person with diverticulosis typically has many diverticula scattered throughout the colon, but diverticula are most common in the sigmoid and descending colon.

Most people with diverticulosis have few or no symptoms. Diverticulosis is not a problem unless a diverticulum ruptures and an infection (abscess) results, a condition called diverticulitis. Diverticulitis causes abdominal pain, fever and tenderness usually in the left lower abdomen. Rarely, bleeding can occur from a diverticulum when a blood vessel inside the diverticulum is weakened by the infection and ruptures.

Bleeding from diverticulosis (diverticular bleeding) without the presence of diverticulitis is painless. Bleeding from diverticulosis is generally more severe and brisker than bleeding from anal fissures, hemorrhoids, and colon tumors. Diverticular bleeding is the most common cause of moderate to severe rectal bleeding that requires hospitalization and blood transfusions among the elderly population in the Western world.

When bleeding occurs in a diverticulum located in the sigmoid colon, the bleeding tends to be bright red. When bleeding occurs in a diverticulum located in the right or ascending colon, the bleeding may also be bright red if the bleeding is brisk and the transit through the colon is rapid; however, the color is more likely to be dark red, maroon, or, sometimes, even black (melena).

Bleeding from diverticulosis is usually brief (it stops on its own). However, diverticular bleeding tends to recur. For example, a patient may experience several episodes of rectal bleeding from diverticula during the same hospitalization. Even after discharge from the hospital, some patients who do not have the diverticula-containing part of their colon surgically removed will experience another episode of diverticular bleeding within 4-5 years.

Picture of diverticular disease (diverticulitis)

Meckel’s diverticulum

A Meckel's diverticulum is an out-pouching (sack) that protrudes from the small intestine near the junction of the small intestine and the colon. It is present from birth and occurs in a small percentage of the population. Some Meckel's diverticula can secrete acid, like the stomach, and the acid can cause ulcerations in the inner lining of the diverticulum or the tissues of the small intestine adjacent to the diverticulum. These ulcers can bleed. Bleeding from a Meckel's diverticulum is the most common cause of gastrointestinal bleeding in children and young adults. Bleeding from a Meckel's diverticulum is painless but can be brisk and can cause bright red, dark red, or maroon stools.

Angiodysplasias

Abnormal collections of enlarged blood vessels frequently occur just under the inner lining of the colon, small intestine or stomach. These abnormal vessels are called angiodysplasias. Angiodysplasias usually can be seen easily during endoscopy as bright red, spider-like lesions just beneath the colon's lining. Although angiodysplasias may occur anywhere in the colon, they are most common in the right or ascending colon. The cause of angiodysplasias is unknown, but they occur with increasing frequency as people grow older. Bleeding from angiodysplasias is painless and can result in bright red, dark red, maroon, or black stools. Angiodysplasias also can cause occult bleeding and iron deficiency anemia.

Colitis and proctitis

Colitis means inflammation of the colon. Proctitis means inflammation of the rectum. Several different diseases can cause colitis and proctitis. These include bacterial or viral infection, ulcerative colitis or proctitis, Crohn's colitis, ischemic colitis, and radiation colitis or proctitis.

Ulcerative colitis, ulcerative proctitis, and Crohn's colitis are chronic inflammatory diseases of the colon due to overactivity of the body's immune system. These diseases can cause abdominal pain, diarrhea, and bloody diarrhea (diarrhea mixed with blood). Occasionally, moderate or severe rectal bleeding may occur. The bleeding originates from ulcerations in the colon.

Like ulcerative colitis and Crohn's colitis, infections – bacterial and, less commonly, viral — can inflame the colon, leading to abdominal pain, diarrhea, and even bloody diarrhea. Rarely, infections may cause moderate or severe rectal bleeding. Examples of infections causing rectal bleeding include Salmonella, Shigella, Campylobacter, C. difficile, E. Coli O157:H7, and cytomegalovirus (the last in individuals with HIV infection).

Ischemic colitis is inflammation of the colon that is caused when the supply of blood to the colon is reduced suddenly. This is most often due to a blood clot that obstructs a small artery supplying blood to a portion of the colon. The sudden reduction in the flow of blood can lead to ulceration of the colon and cause sudden onset of severe lower abdominal, cramping pain followed by rectal bleeding. The most common part of the colon affected by ischemic colitis is the splenic flexure (the part of the colon where the transverse colon joins the left colon). The amount of blood lost during an episode of ischemic colitis usually is small. Rectal bleeding and the abdominal pain of ischemic colitis usually subside on their own after several days. The colonic ulcers usually heal after a few weeks.

Radiation treatment for cancers of the abdomen can cause radiation colitis acutely, but permanent changes to the inner lining of the colon and the colonic blood vessels may occur, which can result in bleeding many years after treatment. A common example is radiation proctitis that results from pelvic radiation for the treatment of prostate cancer. Rectal bleeding from radiation proctitis usually is mild, but occasionally can be chronic enough to cause anemia.

Polypectomy

Colon polyps found during colonoscopy usually are removed, a process called polypectomy. Bleeding can occur at the site of the polypectomy days to weeks after the polyp is removed. Such bleeding is called delayed post-polypectomy bleeding. Smaller polyps (2-3 mm in size) can be removed with biopsy forceps. The amount of blood loss from the use of a forceps usually is minute, and there will be no delayed bleeding. However, larger polyps (larger than 5-10 mm) usually are removed with an electro-surgical snare. These snares are connected to a machine that generates an electrical current. The polyp is looped within a snare, and electrical current is passed through the snare. The electrical current cuts off the polyp and cauterizes ("heat seals") the tissue at the base of the polyps. Cauterization prevents bleeding during polypectomy; however, the site of cauterization heals with the formation of an ulcer. Rarely, these ulcers can bleed several days to up to 2-3 weeks after polypectomy. Post-polypectomy bleeding can at times be brisk and severe, and can be bright red, dark red, maroon colored, or black.

Rare causes of rectal bleeding

Rarely, rapid and severe bleeding from the upper gastrointestinal tract (for example, ulcers of the stomach or duodenum) can cause bright red rectal bleeding. Other rare causes include leaking of larger amounts of blood into the gastrointestinal tract when a blood vessel ruptures. This may occur when an ulcer of the gastrointestinal tract erodes into a nearby artery or when an arterial graft, for example, an aortic graft used to repair an aortic aneurysm, erodes into the gastrointestinal tract. Even more rare is bleeding from a rectal ulcer, or tumors of the small intestine.

What kind of doctor treats rectal bleeding?

Rectal bleeding usually is managed by a gastroenterologist, a colon and rectal surgeon, or a proctologist.

When should I call a doctor for blood in the stool (rectal bleeding)?

Any blood in the stool is not normal and should be reported to a health-care professional. However, there are certain circumstances that might be considered an emergency and medical care should be accessed immediately. These situations include:

Black, tarry stools that may be due to bleeding from the esophagus, stomach or duodenum (upper gastrointestinal [GI] tract). This is especially a potentially serious concern in patients with liver disease and/or portal hypertension who have esophageal varices. This is a potential life-threatening situation.
Maroon colored stool may be caused by an upper GI bleed or a bleeding source in the small intestine.
Lightheadedness, weakness, fainting (syncope), chest pain or shortness of breath may be symptoms of significant blood loss.
Bleeding that is associated with fever and abdominal pain.

How is the cause of blood in the stool (rectal bleeding) diagnosed?

An accurate diagnosis of the location and the cause of rectal bleeding is important for proper treatment, and prevention of further bleeding. Diagnosis relies on the history and physical examination, anoscopy, flexible sigmoidoscopy, colonoscopy, radionuclide scans, angiograms, and blood tests.

History and physical examination

The age of the patient may offer an important clue to the cause of rectal bleeding. For example, moderate to severe rectal bleeding in teenagers and young adults is more likely to come from a Meckel's diverticulum. Moderate or severe rectal bleeding in older individuals is more likely to be due to diverticulosis or angiodysplasias. Mild rectal bleeding in an adult with prior abdominal radiation treatment may be due to radiation proctitis.

The presence or absence of other symptoms also may provide important clues. Bleeding from diverticulosis, angiodysplasias, and Meckel's diverticula usually is not associated with abdominal or rectal pain. Rectal bleeding from ischemic colitis is often preceded by the sudden onset of lower abdominal, crampy pain. Fever, abdominal pain, and diarrhea often occur with colitis due to infection, ulcerative colitis, or Crohn's colitis. Mild bleeding accompanied with pain in the anal area during defecation (passing of stool) suggests bleeding from an anal fissure. A recent change in bowel habit such as increasing constipation or diarrhea suggests the possibility of cancer of the colon.

Inspection of the anus may disclose bleeding from a hemorrhoid or anal fissure. Unfortunately, most hemorrhoids and fissures are not actively bleeding at the time a patient arrives at the doctor's office. Thus, even if a doctor finds a hemorrhoid or anal fissure, he/she cannot be certain that they are the cause of the bleeding. Therefore, flexible sigmoidoscopy or colonoscopy will have to be done to exclude other potentially more serious causes of bleeding.

Anoscopy

An anoscope is a three-inch long, tapering, metal or clear plastic, hollow tube approximately one inch in diameter at its wider end. The anoscope is lubricated, and the tapered end is inserted into the anus, through the anal canal, and into the rectum. As the anoscope is withdrawn, the area where internal hemorrhoids and anal fissures are found is well seen. Straining by the patient, as if they are having a bowel movement, may make hemorrhoids more prominent.

Whether or not hemorrhoids and anal fissures are found, if there has been rectal bleeding, the colon above the rectum needs to be examined to exclude other important causes of bleeding. Examination above the rectum can be accomplished by either flexible sigmoidoscopy or colonoscopy, procedures that allow the doctor to examine approximately one-third or the entire colon, respectively.

Flexible sigmoidoscopy

Flexible sigmoidoscopy utilizes a flexible sigmoidoscope, a fiberoptic viewing tube with a light at its tip. It is a shorter version of a colonoscope. It is inserted through the anus and is used by the doctor to examine the rectum, sigmoid colon and part or all of the descending colon. It is useful for detecting diverticula, colon polyps, and cancers located in the rectum, sigmoid colon, and descending colon. Flexible sigmoidoscopy also can be used to diagnose ulcerative colitis, ulcerative proctitis, and sometimes Crohn's colitis and ischemic colitis.

Despite its value, flexible sigmoidoscopy cannot detect cancers, polyps, or angiodysplasias in the transverse and right colon. Flexible sigmoidoscopy also cannot diagnose colitis that is beyond the reach of the flexible sigmoidoscope. Because of these limitations, colonoscopy may be necessary. The advantage of flexible sigmoidoscopy over colonoscopy is that it can be accomplished with no preparation of the colon or after only one or two enemas.

Colonoscopy

Colonoscopy is a procedure that enables an examiner (usually a gastroenterologist) to evaluate the inside of the entire colon. This is accomplished by inserting a flexible viewing tube (the colonoscope) into the anus and then advancing it slowly under direct vision through the rectum and the entire colon. The colonoscope frequently can reach the part of the small intestine that is adjacent to the right colon.

Colonoscopy is the most widely used procedure for evaluating rectal bleeding as well as occult bleeding. It can be used to detect polyps, cancers, diverticulosis, ulcerative colitis, ulcerative proctitis, Crohn's colitis, ischemic colitis, and angiodysplasias throughout the entire colon and rectum.

If there is any possibility that the bleeding is coming from a location above the colon, and esophagogasatroduodenal endoscopic examination (EGD) also should be done to identify or exclude an upper gastrointestinal source of bleeding.

Video capsule and small intestine endoscopy

If neither an upper or lower gastrointestinal source of blood in the stool is found, the small intestine becomes suspect as the source of the bleeding. There are two ways of examining the small intestine. The first is the video capsule, a large pill containing a miniature camera, battery and transmitter that is swallowed and relays photos of the small intestine wirelessly to a recorder carried over the abdomen. The second way to examine the small intestine is with a specialized endoscope similar to the endoscopes used for upper gastrointestinal endoscopy and colonoscopy. The advantage of these endoscopes over the video capsule is that bleeding lesions can be biopsied and treated, something that can't be done with the capsule. Unfortunately, small intestinal enteroscopy is time consuming and not generally available. Patients often must be sent to centers where small intestinal enteroscopy is available.

Radionuclide scans

There are two types of radionuclide scans that are used for determining the site of gastrointestinal bleeding; a Meckel's scan, and a tagged red blood cell (RBC) scan.

The Meckel's scan is a scan for detecting a Meckel's diverticulum. A radioactive chemical is injected into the patient's vein, and a nuclear camera (like a Geiger counter) is used to scan the patient's abdomen. The radioactive chemical will be picked up and concentrated by the acid-secreting tissue in the Meckel's diverticulum and will appear as a "hot" area in the right lower abdomen on the scan.

Tagged RBC scans are used to determine the location of the gastrointestinal bleeding. After drawing blood from the bleeding patient, a radioactive chemical is attached to the patient's red blood cells and the "tagged" red blood cells are injected back into the patient's vein. If there is active gastrointestinal bleeding, the radioactive red blood cells leak into the intestine where the bleeding is occurring and will appear as a hot area with a nuclear camera. One drawback of the tagged RBC scan is that bleeding will not show as a hot area if there is no active bleeding at the time of the scan. Thus, it can fail to diagnose the site of bleeding if bleeding is intermittent and the scan is done between bleeding episodes. Another drawback of the scan is that it requires a reasonable amount of bleeding to form a hot area. Thus, it can fail to diagnose the site of the bleeding if bleeding is too slow. The tagged RBC scan is safe, and can be done quickly and without discomfort to the patient.

Unfortunately, the tagged RBC scans are not very accurate in defining the exact location of the bleeding; there is often a poor correlation between where the tagged RBC scan shows the bleeding to be and the actual site of bleeding found at the time of surgery. Therefore, tagged RBC scans cannot be relied upon to help surgeons decide what area of the gastrointestinal tract to remove in the event the bleeding is severe or persistent and requires surgery. However, if the scan shows a hot area, it usually means there is active bleeding, and the patient may be a candidate for a visceral angiogram to more accurately locate the site of bleeding.

Visceral angiogram

A visceral angiogram is an X-ray study of the blood vessels of the gastrointestinal tract. The doctor (usually a specially trained radiologist) will insert a thin, long catheter into a blood vessel in the groin and, under X-ray guidance, will advance the tip of the catheter into one of the mesenteric arteries (arteries that supply blood to the gastrointestinal tract). A radio-opaque dye is injected through the catheter and into the mesenteric artery. If there is active bleeding, the dye can be seen leaking into the gastrointestinal tract on the X-ray film. Visceral angiograms are accurate in locating rapid bleeding in the gastrointestinal tract, but it is not useful if the bleeding is slow or has stopped at the time of the angiogram.

The visceral angiogram is not widely used because of its potential complications such as kidney damage from the dye, allergic reactions to the dye, and the formation of blood clots in the mesenteric arteries. It is reserved for patients who have severe and continuous bleeding and in whom colonoscopy cannot locate the site of the bleeding.

MRI and CT tomographic angiography

Magnetic resonance imaging (MRI) and CT scan can both be used in a manner similar to X-rays in visceral angiography, a diagnostic procedure that has been discussed previously. The use of MRI and CT angiography for diagnosis in gastrointestinal bleeding is a relatively recent development, and their value has not been clearly defined. They could be considered experimental.

Nasogastric tube aspiration

If there is concern about bleeding coming from the stomach or duodenum, nasogastric tube aspiration can be done. A thin, flexible rubber or plastic tube is passed through the nose and into the stomach. The liquid contents of the stomach then are aspirated and examined for visible blood. (The contents also can be tested for occult blood.) If the bleeding is coming from the stomach, there may be visible blood in the aspirate. There also may be visible blood if the bleeding is coming from the duodenum if some of the blood leaks retrograde back into the stomach. The main difficulty in interpreting results of aspiration is that there may be no blood if the bleeding has stopped even temporarily. Therefore, the absence of blood in the aspirate cannot completely exclude the stomach as the source of the bleeding. Only esophagogastroduodenoscopy can exclude causes of upper gastrointestinal bleeding.

Esophagogastroduodenoscopy

If there is major concern about bleeding coming from the esophagus, stomach or duodenum, an esophagogastricduodenoscopy (EGD) can be done using an endoscope similar to the endoscope used for colonoscopy.

Blood tests

Blood tests such as a complete blood count (CBC) and iron levels in the blood play no role in locating the site of gastrointestinal bleeding; however, the CBC and blood iron levels may help to determine whether bleeding is acute or chronic, since an anemia (low red blood cell count) associated with iron deficiency suggests chronic bleeding over many weeks or months. Colonic conditions commonly causing iron deficiency anemia include colon polyps, colon cancers, colon angiodysplasias, and chronic colitis.

When a patient loses a large amount of blood suddenly, as with moderate or severe acute rectal bleeding, the lost blood is replaced by fluid from the body's tissues. This influx of fluid dilutes the blood and leads to anemia (a reduced concentration of red blood cells). It takes time, however, for the tissue fluid to replace the lost blood within the blood vessels. Therefore, soon after a sudden episode of major bleeding, there may be no anemia. It takes many hours and even a day or more for the anemia to develop while tissue fluid slowly dilutes the blood. For this reason, a red blood cell count early after bleeding is not reliable for estimating the severity of the bleeding.

What is the treatment for rectal bleeding (blood in the stool)?

Treatment and management of rectal bleeding include

correcting the low blood volume and anemia;
diagnosing the cause and the location of the bleeding;
stopping active bleeding and preventing rebleeding; and
Looking for other nonbleeding lesions that may bleed in the future.

Correcting low blood volume and anemia

Moderate to severe rectal bleeding can cause the loss of enough blood to result in weakness, low blood pressure, dizziness, or fainting, and even shock. Patients with these symptoms usually are hospitalized. They need to be quickly treated with intravenous fluids and/or blood transfusions to replace the blood that has been lost so that diagnostic tests such as colonoscopies and angiograms can be performed safely to determine the cause and location of the bleeding.

Patients with severe iron deficiency anemia may need hospitalization for blood transfusions followed by prolonged treatment with oral iron supplements (tablets). Patients with iron deficiency anemia as a result of chronic gastrointestinal blood loss should undergo tests (such as colonoscopy) to determine the cause of the chronic blood loss.

Unless anemia is severe, patients with mild rectal bleeding from colon polyps, colon cancers, anal fissures, and hemorrhoids usually do not need hospitalization. Mild anemia can be treated with oral iron supplements while tests are performed to diagnose the cause of bleeding.

Determining the cause and location of bleeding

Colonoscopy is the most widely used procedure for the diagnosis and treatment of rectal bleeding. Most colonoscopies are performed after administration of oral laxatives to cleanse the bowel of stool, blood, and blood clots. However, in emergency situations such as when the bleeding is severe and continuous, a doctor may choose to perform an emergency colonoscopy without first cleansing the large bowel. In trained and experienced hands, the risk of either elective (delayed) or urgent colonoscopy is small. (Colon perforation, the most common complication, is rare). The benefits usually far outweigh the potential risks.

Colonoscopy is useful for both diagnosing the cause and determining the location of the bleeding. Locating the site of bleeding is especially important in diverticular bleeding. Even though most diverticular bleeding stops spontaneously without the need for surgery, patients with severe, recurrent, or continuous diverticular bleeding may need surgery to remove the bleeding diverticulum. Since a patient typically has numerous diverticula scattered throughout the colon, colonoscopy may be able to determine which diverticulum is bleeding prior to surgery. Without an accurate knowledge of the location of the bleeding diverticulum, the surgeon may have to perform an extensive colon resection (which is not as desirable as removing a small section of the colon) in order to make sure that the bleeding diverticulum is removed.

Nevertheless, colonoscopy has limitations. During colonoscopy doctors may not find active bleeding from a specific diverticulum. He/she may only find a colon filled with blood along with scattered diverticula. In such situations, the diagnosis of diverticular bleeding is assumed if no other cause for the bleeding such as colitis or colon cancer is found. In these situations, there is always some uncertainty about the location of the bleeding. Small, bleeding angiodysplasias also may be difficult to see and may be missed in a colon filled with blood. This is when radionuclide scans and visceral angiograms may be helpful. If the patient starts bleeding again, an urgent, tagged RBC scan followed by a visceral angiogram may demonstrate the location of the bleeding.

Colonoscopy also cannot positively diagnose bleeding from a Meckel's diverticulum because the colonoscope usually cannot reach the part of the small intestine in which the Meckel's diverticulum is located. But colonoscopy still can be helpful in establishing the diagnosis of a bleeding Meckel's diverticulum. Thus, in a young patient with rectal bleeding, a colonoscopy showing a blood filled colon without another source of bleeding, particularly if accompanied by an abnormal Meckel's scan, makes the diagnosis of Meckel's diverticulum bleeding highly likely. Surgical resection of the Meckel's diverticulum should result in permanent cure with no recurrence of bleeding.

Stopping bleeding and preventing rebleeding

Colonoscopy is more than just a diagnostic tool; it can also be used to stop bleeding by removing (snaring) bleeding polyps, by cauterizing (sealing with electrical current) bleeding angiodysplasias or postpolypectomy ulcers and, occasionally, by cauterizing actively bleeding blood vessels inside diverticula. Cauterization during colonoscopy is usually accomplished by inserting a long cauterizing probe through the colonoscope. Colonoscopy with cauterization has been used to stop bleeding in many patients with bleeding from diverticula or angiodysplasias, thereby decreasing their need for blood transfusions, shortening their hospital stays, and avoiding surgery.

When colonoscopy cannot identify the site of bleeding or is unable to stop recurrent or continuous bleeding, visceral angiograms may be helpful. When a bleeding site is identified by an angiogram, medications can be infused through the angiographic catheter to constrict the bleeding blood vessel and stop the bleeding, Microscopic coils also can be infused through the catheter to plug (embolize) the bleeding blood vessel, thereby stopping the bleeding.

If colonoscopy and visceral angiogram cannot stop continuous bleeding or prevent rebleeding, then surgery becomes necessary. Ideally, the site of bleeding has been identified by colonoscopy, nuclear scans, or visceral angiogram, so that the surgeon can target the site of bleeding for exploration and excision. For example, a surgeon can usually resect a colon cancer, a bleeding polyp, or a Meckel's diverticulum with precision. Sometimes, the exact site of bleeding cannot be established, and the surgeon will have to perform an extensive colon resection under the presumption that a diverticulum or angiodysplasia is the cause of the bleeding.

Mild rectal bleeding from anal fissures and hemorrhoids usually can be treated with local measures such as sitz baths, hemorrhoidal creams, and stool softeners. If these measures fail, several nonsurgical and surgical treatments are available.

Is it possible to prevent rectal bleeding (blood in the stool)?

Most diseases that cause rectal bleeding are likely preventable, but it often is not possible.

Hemorrhoids can be avoided with proper diet and by prevention of constipation and straining to pass stool, but normal pregnancy increases the risk of hemorrhoid formation as does the acute diarrheal illness.
Avoiding constipation is believed to decrease the risk of diverticulosis, outpouchings in the lining of the colon, and the risk of a diverticular bleed.
Alcohol abuse increases the risk of rectal bleeding in a variety of ways, from directly irritating the lining of the gastrointestinal (GI) tract, to decreasing clotting capabilities of blood.

What is the prognosis of rectal bleeding (blood in the stool)?

The prognosis depends upon the underlying cause of the bleeding. Fortunately, the cause of rectal bleeding often is benign, and due to hemorrhoids or an anal fissure.

It is important to never ignore blood in the stool or rectal bleeding. It may be a clue to a serious illness and the earlier a diagnosis can be made, the better the chance for a cure.

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