Black Stool

What is Black Stool?

The normal color of stool, which can range from brown to golden-brown, is attributed to the elimination of bilirubin in the gastrointestinal tract. Any changes in the stool color signifies both internal and external changes in the body. Internal factors include food or medicine intake, while external factors include any underlying medical conditions.

black stool colors

Picture 1 – Different Colors of Stool with Brown as the Normal Color

Black stool, for instance, is darkened stool. It is sometimes called melena, but the latter focuses more on bleeding as the cause. The occurrence of black stool does not usually mean that there is a bleeding in the gastrointestinal tract. Sometimes it is caused by eating foods that leave a dark residue in the stool. However, it should be checked by a physician to assess the complete history of the patient, including diet and any medications to rule out internal bleeding. If black stool is not attributed to benign causes such as food intake, then internal bleeding may be considered.
black stool image
Picture 2 – Black Stool

Black Stool Causes

As discussed earlier, black stool can be caused by both external and internal factors. These include:

External or benign causes

Black stool caused by benign conditions is called “false melena” because the darkened stool is not caused by blood. These conditions include the following:

  1. Intake of foods such as blueberries, black licorice, and too much chocolate. Generally, foods that are black, green, or dark blue in color may lead to dark orblack stools.
  2. Intake of lead
    3. Intake of iron as dietary supplement or part of of iron-deficiency anemia treatment
    4. Intake of medications such as bismuth subsalicylate (pepto-bismol)

False melena can also be seen in newborn infants who have swallowed maternal blood during delivery. This is not associated with bleeding inside the newborn and is resolved after all the blood has been eliminated.

Internal causes or bleeding

Serious causes of black stool include internal bleeding in the upper gastrointestinal system (from the esophagus to the duodenum). On the one hand, stools are often black in color because the blood has traveled from the upper to the lower gastrointestinal tract until the waste matter has evacuated in the stools. During this process, the blood has already coagulated. Melena refers to black, tarry stools which are caused by bleeding. Bright red stools, on the other hand, signify fresh blood coming out from the lower gastrointestinal system. The following conditions cause black, tarry stools:

Bleeding ulcer

Peptic ulcer disease causes a sore or open wound in the stomach or duodenum. This is usually caused by infection with the Helicobacter pylori bacteria. Ulcers can also result from physical, psychologica,l and emotional stress which increases the production of gastric acids that irritate and injure the stomach lining. Moreover, prolonged use of non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, aspirin, naproxen, and mefenamic acid decrease the protective coating of the stomach lining, causing injury to the area. These over-the-counter medications should be used cautiously to prevent ulcers.


Gastritis is the inflammation of the gastric mucosa. This usually results from smoking and alcoholic beverage consumption. It can also result from other diseases such as bile reflux and pernicious anemia. When the stomach is inflamed, it may lead to further irritation and cause bleeding.

Esophageal varices

These are varicosities or dilated veins on the esophagus as a result of portal hypertension (high blood pressure in the hepatic circulation) and liver cirrhosis. When the varices rupture, they cause profuse bleeding in the upper gastrointestinal tract, causing melena or coffee ground emesis (dark vomitus). Treatment includes placement of balloon catheters to compress the bleeding veins.

Mallory-Weiss tear

Mallory-Weiss tear is a tear in the lower esophagus adjoining the stomach due to violent vomiting, convulsions, or coughing. This is a rare condition but causes serious hemorrhage.

Hemorrhagic fever

This disease is caused by a virus carried by mosquitoes which attack the platelets. With reduced platelets in the body, blood aggregation and coagulation are impaired, causing profuse bleeding not only in the upper gastrointestinal system but also in all areas of the body.

Black Stool Symptoms

Symptoms of black stool include very dark stool, maybe as black as charcoal, depending on the cause. Black stools due to benign causes may be dark, but profuse bleeding in the stomach and esophagus may lead to darker feces. Furthermore, tarry stools may also be due to contact with digestive juices. Associated symptoms caused by internal bleeding may also be present such as:

  1. Abdominal distention
  2. Paleness
  3. Fatigue
  4. Shortness of breath
  5. Hypotension
  6. Tachycardia (fast heart beat)

When these symptoms appear, it is usually a sign of profuse hemorrhage that needs emergency action.

Black Stool Diagnosis

Diagnosing melena includes a thorough medical history and series of diagnostic tests. A medical history is essential to determine the dietary pattern of the patient that may cause black stools and to check any prolonged use of NSAIDs or other medications which may lead to black stools. When black stools are not associated with benign causes, laboratory studies are done such as:

Fecal occult blood test

This test determines any presence of red blood cells in the stool. The test involves collecting a stool sample (usually the whole stool) and checking blood under the microscope.
When blood is positive in the stool, a series of tests is also done to determine the underlying cause and any complications.

Barium studies (upper gastrointestinal series)

Barium studies involve taking x-rays of the upper gastrointestinal tract after ingestion of barium solution. This test allows the examiner to assess any obstruction or ulcerations in the area.

Esophagogastroduodenoscopy (EGD)

EGD involves the use of a small camera that passes through the patient’s mouth; this permits visualization of the esophagus, stomach, and duodenum. It is an accurate test to see if there are any ulcerations and varicosities in the area.

Blood test

Blood tests are done to assess reduction in the RBCs, hemoglobin, and hematocrit as a result of bleeding.

Black Stool Treatment

Black stool is not a disease that needs to be treated. The underlying disease needs to be managed to stop the bleeding and eradicate black stools. Treatment depends on the cause, and there are several managements to do so.
False melena can be treated by eradicating the main source; although foods and supplements are not a concern, patients are simply instructed to eat certain foods and take iron supplements.
Treatment is directed on internal causes. Ulcers and gastritis are managed by the use of gastric protectants to prevent further bleeding. Soft diet is advised to avoid irritation and further inflammation. Esophageal varices are managed through insertion of catheter balloons to stop the bleeding. Gastric lavage (washing) is also done with the use of cold saline solution to constrict the blood vessels in the area and to stop the bleeding.
In cases of hypovolemia due to profuse bleeding, blood transfusion is initiated.

Black Stool Complications

False melena does not result in any complications. However, melena due to bleeding may result in the following:

  1. Hypovolemia
  2. Anemia
  3. Excess fatigue and weakness
  4. Cardiovascular collapse due to hypovolemia

Once black stool is observed, medical consultation should be done to prevent such life-threatening complications.

Black Stool Prevention

Melena can be easily prevented by avoiding risk factors which may lead to bleeding of the upper gastrointestinal system. They include:

  1. Avoidance of prolonged use of anti-inflammatory drugs. When they are needed, it is advisable to take the medication on a full stomach or after meals to prevent gastric irritation.
  2. Smoking cessation to prevent gastritis and ulcers. Smoking irritates the gastric lining.
  3. Limited consumption of alcohol and other irritating foods. Excessive alcohol intake leads to irritation of the esophagus and stomach.
  4. Consumption of green leafy vegetables, fruits, and other foods rich in fiber such as wheat and bran to prevent gastric irritation.
  5. Performance of stress reduction activities and avoidance of stress to prevent excessive production of hydrochloric acid in the stomach.
  6. Avoidance of skipped meals. An empty stomach becomes very prone to irritation due tof gastric acids.

Black Stool Pictures

black stool images

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