Black stool can be a startling observation that prompts immediate concern about internal bleeding. The color change indicates the stool contains either a dark substance ingested through diet or medication, or potentially, blood that has been digested. When the cause is medical, it can signal a serious issue requiring prompt attention, while non-medical causes are generally temporary and harmless. Understanding the texture and accompanying symptoms is the first step in determining the urgency of the situation.
Non-Medical Reasons for Black Stool
The most common causes of dark discoloration are related to substances consumed, which turn the stool black without an underlying medical problem. This type of black stool is typically uniform in color and lacks the sticky, tar-like consistency and foul odor associated with digested blood. The discoloration usually resolves quickly once the causative substance leaves the digestive system.
A frequent culprit is the use of iron supplements, often prescribed to treat anemia. The iron that is not absorbed reacts with sulfur compounds as it passes through the gut, creating black iron sulfide, which darkens the stool. Similarly, medications containing bismuth subsalicylate, used for indigestion and diarrhea, cause temporary darkening. Bismuth reacts with trace amounts of sulfur to form the black compound bismuth sulfide.
Consuming certain dark-colored foods can also result in temporary black stools. Examples include black licorice, blueberries, blood sausage, or dark chocolate sandwich cookies. The natural pigments or dyes in these items stain the stool, but this effect is benign. Stool discoloration from these sources is generally solid and not sticky, distinguishing it from medical causes.
Understanding Melena and Medical Urgency
The term melena refers specifically to black, tarry, and foul-smelling stool, which signals bleeding in the upper gastrointestinal (GI) tract. The characteristic color and sticky texture occur because the blood has been partially broken down by digestive enzymes and acid. This digestion process changes red hemoglobin into a black-pigmented compound, giving the stool its distinct appearance and strong, metallic odor.
Bleeding in the upper GI tract (esophagus, stomach, and duodenum) is most frequently caused by peptic ulcers. Other sources include inflammation of the stomach lining (gastritis), tears in the esophagus from severe vomiting (Mallory-Weiss tears), or enlarged, fragile veins (esophageal varices), often associated with liver disease. Melena signifies active or recent internal bleeding and represents a high-urgency medical situation.
Immediate medical attention is necessary if black stool is accompanied by symptoms such as lightheadedness, dizziness, fainting, or signs of shock, which indicate significant blood loss. Severe abdominal pain, vomiting blood, or sudden weakness are also critical warning signs that require emergency evaluation. In these cases, the body is reacting to an acute loss of blood volume, and the underlying cause must be identified and treated without delay.
Diagnostic Steps and Treatment Strategies
When medical causes are suspected, diagnosis focuses on locating the source of the bleeding. After a physical exam and initial blood tests, an upper endoscopy, or esophagogastroduodenoscopy (EGD), is the primary diagnostic and therapeutic procedure. The EGD involves passing a flexible tube with a camera through the mouth to examine the lining of the esophagus, stomach, and duodenum, allowing the physician to visualize the bleeding source directly.
Endoscopic Hemostasis
The EGD is often used therapeutically to achieve hemostasis, the immediate cessation of bleeding. Various endoscopic techniques are employed. Injection therapy involves injecting a solution, such as diluted epinephrine, directly into the bleeding site to constrict the blood vessel. Mechanical methods, like applying small endoscopic clips (endoclips), clamp the vessel shut to physically stop the blood flow. Thermal coagulation uses heat delivered through a probe to cauterize the tissue and seal the vessel.
Long-Term Management
Once immediate bleeding is controlled, long-term treatment addresses the underlying cause to prevent recurrence. For peptic ulcers, a common source of melena, treatment involves high-dose acid-reducing medications, such as proton pump inhibitors (PPIs), to allow healing. If the ulcer is caused by the bacterium Helicobacter pylori, a course of antibiotics combined with a PPI is administered to eradicate the infection. Patients who must continue taking nonsteroidal anti-inflammatory drugs (NSAIDs) may be prescribed a maintenance dose of a PPI to protect the stomach lining and minimize the risk of future bleeding.