If the poop is black, it means melena. Black stool means several possibilities:

1. The patient has used pig blood, duck blood, etc., or has taken iron supplements, which can lead to similar black stools.

2. Patients who have taken bismuth citrate or activated carbon and other charcoal tablets can also make their stool black. But this kind of black stool is often not black but shiny. The patient also has no symptoms of upper gastrointestinal bleeding, such as upper abdominal pain, dizziness, sweating, soft hands and other blood loss conditions. Often we can make the identification based on the patient's medical history and corresponding symptoms.

3. Upper gastrointestinal bleeding. The upper gastrointestinal tract refers to the section of the digestive tract from the esophagus to the duodenum. Bleeding in this section of the digestive tract is often black. When upper gastrointestinal tracts such as the esophagus, stomach, duodenum, upper jejunum, pancreas and biliary tract bleed, the iron in hemoglobin in red blood cells combines with sulfide under the action of intestinal bacteria to form iron sulfide, which makes the stool black. This kind of black stool is dark and shiny, and looks like tar, so it is also called tarry stool.