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Stool characteristics that cause angst in patients and parents prompting emergency department visits include changes in color (black, red, white, green, blue), consistency (hard, loose, watery), or frequency (too often, too infrequent) and associated pain.
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Melena is a dark maroon (see Fig. 25.36) to black tar-like (see Fig. 25.37 and Fig 25.38) stool typically due to upper gastrointestinal (GI) bleeding of 100 to 200 mL of blood. Melena can occur from lower GI bleeds with delayed transit, swallowed blood from maternal mammary bleeding, epistaxis, or hemoptysis. Substances that cause black stool that are negative for occult blood include iron supplements, bismuth preparations, activated charcoal, and blueberries.
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Bright red bloody stool (hematochezia) suggests lower GI bleeding and can be caused by colonic polyps, colon cancer, diverticulosis, anal fissures, hemorrhoids, inflammatory bowel disease, aortoenteric fistula, arteriovenous malformations, infectious diarrhea, and coagulopathy. Causes in children include necrotizing enterocolitis, malrotation with midgut volvulus, Hirschsprung disease, milk-protein allergy, intussusception (see Fig. 25.39), Meckel diverticulum, GI duplication cysts, vasculitis, hemolytic uremic syndrome, rectal ulcers, and juvenile polyps (see Fig. 25.40). Causes of red but not bloody stool include cefdinir (see Fig. 25.41), spicy food dyes, red licorice, beets, and red-colored food dyes.
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