Melena refers to dark, tarry stools, typically signaling bleeding in the upper gastrointestinal (GI) tract. This distinct appearance results from blood being altered by digestive enzymes and stomach acid as it travels through the digestive system. Recognizing melena is important because it indicates internal bleeding that requires prompt medical attention and further diagnostic investigation.
Recognizing Initial Clues
The characteristic appearance of melena is black, sticky, and tarry, often with a strong, offensive odor. Its dark color arises from the digestion of hemoglobin by intestinal enzymes and bacteria. Individuals experiencing melena may also report symptoms like weakness, fatigue, dizziness, or lightheadedness, which can indicate significant blood loss. Abdominal pain or cramps might also accompany melena, depending on the underlying cause. A healthcare provider’s initial assessment includes a physical examination, checking for signs of anemia such as pale skin or changes in vital signs, which suggest internal bleeding.
Laboratory Confirmation Methods
Confirming the presence of blood in stool and assessing its impact relies on several laboratory tests. The Fecal Occult Blood Test (FOBT) is a chemical test designed to detect hidden blood in stool samples. This test works by detecting the peroxidase activity of hemoglobin; however, it can yield false positive results due to dietary factors like red meat or certain raw vegetables, and some medications.
A more modern and specific alternative is the Fecal Immunochemical Test (FIT), which detects human hemoglobin using antibodies. FIT is preferred over FOBT because it is not affected by dietary restrictions and offers improved sensitivity and specificity. While these stool tests confirm the presence of blood, a Complete Blood Count (CBC) is also a routine part of the diagnostic process. A CBC measures hemoglobin and hematocrit levels, providing an indirect but crucial indication of anemia, which often accompanies significant blood loss.
Locating the Bleeding Source
Once melena is suspected or confirmed, identifying the precise location of the bleeding is paramount for effective treatment.
Endoscopic Procedures
Upper endoscopy (EGD) is a primary procedure for this purpose. During an upper endoscopy, a thin, flexible tube equipped with a camera is guided down the esophagus, allowing direct visualization of the esophagus, stomach, and duodenum to locate bleeding sources. This procedure can also facilitate immediate treatment, such as sealing bleeding vessels. While melena usually points to an upper GI source, a colonoscopy may be performed if upper endoscopy is inconclusive or lower GI bleeding is suspected. A colonoscopy involves a similar flexible tube inserted into the rectum to examine the large intestine.
Advanced Imaging Techniques
If the bleeding source remains obscure despite these endoscopic procedures, other advanced imaging techniques may be utilized. Capsule endoscopy involves swallowing a small, pill-sized camera that captures images as it travels through the small bowel, transmitting them to an external recorder. This method is useful for detecting lesions in the small bowel, which traditional endoscopes cannot easily reach. CT angiography (CTA) can also be employed, especially in acute bleeding, to rapidly identify the bleeding site by visualizing contrast extravasation from blood vessels. This technique helps pinpoint the exact location of hemorrhage, guiding interventions like embolization or surgery.