black tarry stool

Stool that is viscid and blackened by oxidized blood, a finding often caused by cancer-related occult haemorrhage; BTSs appear with as little as 50–75 mL of blood, usually above the ligament of Treitz; oxidation of haeme by combined action of enzymes and bacteria requires several hours
DiffDx Drugs—e.g., salicylates, steroids, rauwolfia, phenylbutazone, indomethacin—which may cause GI blood loss in normal persons and in those with underlying GI tract anomalies. Black tarry may also be iatrogenic—charcoal, iron, bismuth

black tarry stool

Black stool Stool that is viscid and blackened by oxidized blood, a finding often caused by cancer-related occult hemorrhage; BTSs appear with as little as 50-75 mL of blood, usually above the ligament of Treitz–oxidation of heme by combined action of enzymes and bacteria requires several hrs DiffDx Drugs–eg, salicylates, steroids, rauwolfia, phenylbutazone, indomethacin, which may cause GI blood loss in normal persons and in those with underlying GI tract anomalies; BS may also be iatrogenic–charcoal, iron, bismuth