Tarry stool, medically termed Melena, is a distinct and serious symptom signaling a health issue that requires immediate attention. The presence of black, sticky feces is typically evidence of internal bleeding in the upper digestive tract. This appearance results from blood being partially digested, which changes its color and texture before excretion. Melena demands prompt medical evaluation to determine and address the source of the bleeding.
Visual Characteristics of Tarry Stool
True tarry stool is characterized by a jet-black color, often compared to pitch or road tar. Its most distinguishing feature is a sticky, viscous consistency that makes it dense and difficult to flush. This texture is a direct result of the chemical breakdown of blood as it travels through the intestines.
The unique appearance is usually accompanied by a distinctly foul and pungent odor. This powerful smell results from digestive enzymes and intestinal bacteria acting upon the hemoglobin in the blood. The combination of the specific color, tarry consistency, and intense odor defines Melena and differentiates it from simple dark stools.
Understanding the Primary Cause: Upper GI Bleeding
The formation of Melena points to bleeding high up in the gastrointestinal (GI) tract, including the esophagus, stomach, or duodenum. The blood must remain in the GI tract for an extended period, allowing exposure to stomach acid and digestive enzymes.
As the blood moves through the system, hemoglobin is chemically altered and oxidized, turning the normally red iron compound black. This color change typically requires a minimum of 50 to 100 milliliters of blood. Common causes of upper GI bleeding include peptic ulcers (the most frequent cause) and gastritis (inflammation of the stomach lining). Other serious causes are esophageal varices (swollen veins) and Mallory-Weiss tears (tears in the esophageal lining caused by severe vomiting).
Dietary and Medication-Related Black Stool
It is important to distinguish true Melena from non-bleeding causes that simply stain the stool black. Several common items can mimic the color of tarry stool without carrying the same medical urgency. These factors do not involve digested blood and typically lack the sticky consistency and foul odor characteristic of Melena.
Iron supplements are a common culprit, as unabsorbed iron reacts in the digestive tract to create a dark stool. Medications containing bismuth subsalicylate, such as Pepto-Bismol, also cause black stool when the bismuth reacts with sulfur in the digestive system. Certain dark foods, including black licorice, blueberries, and activated charcoal, can also temporarily darken the feces.
Medical Evaluation and Treatment Protocol
Anyone who notices black, tarry, foul-smelling stool should contact a healthcare provider immediately, as this symptom indicates internal bleeding. Emergency care should be sought if the black stool is accompanied by dizziness, fainting, rapid heart rate, or significant abdominal pain, signaling substantial blood loss. The diagnostic process begins with a physical examination and a detailed review of recent medications and diet.
Blood tests check for signs of anemia, indicating blood loss, and assess overall health and clotting status. A fecal occult blood test confirms the presence of blood in the stool, distinguishing Melena from a simple dietary color change. The definitive way to locate the bleeding source is usually an upper endoscopy, or esophagogastroduodenoscopy (EGD).
During an EGD, a flexible tube with a camera visualizes the esophagus, stomach, and duodenum. This procedure is both diagnostic and therapeutic, as a physician can often stop the bleeding immediately by applying heat (electrocautery), injecting medication, or placing a clip on the vessel. For severe blood loss, initial treatment focuses on stabilizing the patient, which may involve administering intravenous fluids or a blood transfusion. Medications such as proton pump inhibitors are commonly prescribed to reduce stomach acid production, helping ulcers heal and preventing further damage.