In patients with abdominal pain, which symptom is most concerning for potential gastrointestinal bleeding?

Black tarry stools, also known as melena, are a significant indicator of potential gastrointestinal bleeding. This symptom results from the digestion of blood as it passes through the gastrointestinal tract, typically indicating that there is bleeding occurring higher up in the digestive system, such as in the stomach or small intestine. The color and consistency signal the presence of oxidized iron in the blood, which is altered by digestive enzymes and acids, making it black and tarry in appearance.

In contrast, loss of appetite, low-grade fever, and lightheadedness can be associated with a variety of conditions, some of which may not necessarily relate to gastrointestinal bleeding. While these symptoms can signal issues requiring medical attention, they are less specific than melena in indicating the presence of active bleeding. Thus, when evaluating abdominal pain, the presence of black tarry stools is the most concerning symptom.