Which symptom is commonly associated with an upper gastrointestinal bleed?

Melena is a symptom that is specifically associated with upper gastrointestinal bleeding. It refers to the passage of dark, tarry stools, which occur when blood from the upper GI tract, such as the esophagus, stomach, or duodenum, is digested by the intestinal enzymes. The dark color results from the breakdown of hemoglobin in the blood, and the tarry appearance indicates that the blood has been present in the digestive tract for a sufficient amount of time for digestion to occur.

In contrast, other options like hematuria—blood in urine—are related to urinary tract issues rather than gastrointestinal bleeding. Diarrhea can occur for a variety of reasons, including infections, irritable bowel syndrome, or other gastrointestinal conditions, but it is not specifically indicative of upper GI bleeding. Constipation is related to bowel movement frequency and consistency and does not suggest any bleeding, upper or lower gastrointestinal. Thus, melena is the hallmark symptom that signifies the presence of an upper GI bleed, making it the correct choice in this context.