The term melanotic stool is sometimes used to refer to black, tarry stools or blood in the stool. Also, melanotic stools may indicate a digestive symptom disorder or injury. Although black, tarry stools often indicate the presence of blood in the stool, a condition called hematochezia also refers to brown or red stools. In general, blood in the stool can originate anywhere in the digestive tract, from the mouth to the anus. Technically, the correct term for this is melenic stool, rather than melanotic stool, but the two terms are often confused.
In general, melanotic stools indicate that the blood originates from the upper part of the gastrointestinal tract. This part of the gastrointestinal system includes the esophagus, the beginning of the small intestine, and the stomach. When stools take on a tarry appearance, it means they have been exposed to digestive juices. Sometimes stomach ulcers caused by certain medications can cause bleeding from the upper GI tract.
Bright red stools usually indicate that the blood originates from the lower gastrointestinal tract, which includes the rectum, large intestine, and anus. Certain conditions like diverticulosis and hemorrhoids can cause frank blood in the stool. Infrequently, abnormal blood vessels and tumor formation can cause lower gastrointestinal bleeding. Sometimes rapid or massive stomach bleeding can cause bright red stools. Certain medications such as Pepto-Bismol® and iron supplements can cause melanotic stools, which are usually transient and harmless.
Sometimes certain foods can cause melanotic stools. These foods include black licorice and blueberries or blackberries. Tomatoes and beets can mimic the appearance of blood in the stool, and in cases like these, a doctor may perform a stool test to rule out melena. Other causes of melanotic stools are gastritis, which is an inflammation of the lining of the stomach, and intestinal ischemia. Typically, intestinal ischemia causes the intestines to lack adequate blood flow, causing bleeding. Rarely, a foreign body or trauma to the gastrointestinal tract can produce melenic stools.
Treatment for melanotic stools depends on the cause. Determining the source of blood in the stool requires a complete physical exam and possibly blood tests that include a complete blood count. Melena can cause anemia, which may be indicated by a decrease in red blood cells. Other diagnostic tests may include an upper and lower GI series, ultrasound, and stool sample testing. While blood in the stool may indicate a harmless condition, other more sinister conditions must be ruled out before a diagnosis can be effectively made.