Q: What amount of blood is enough to manifest melena?
A) 5 mL
B) 10 mL
C) 50 mL
D) 100 mL
E) 250 mL
The objective of the above question is to highlight the point that the severity of gastrointestinal (GI) bleed cannot be predicted due to the presence of black tarry stool, known as melena. The only thing it signifies is that the location of blood is probably proximal to the ligament of Treitz, if obvious ENT source is excluded.
Instead, of melena, if hematochezia i.e. maroon-colored stool is observed, it is probably due to lower GI bleeding or massive upper GI bleeding.
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2. Jensen DM, Machicado GA. Diagnosis and treatment of severe hematochezia. The role of urgent colonoscopy after purge. Gastroenterology 1988; 95:1569.