A 22-month-old boy is brought to the emergency department by his parents after passing two large, maroon-colored stools over the past 18 hours. His mother reports that he has been slightly more tired than usual today, though he has not cried during bowel movements or appeared to be in abdominal pain. She recalls noticing a small amount of dark red blood in his diaper once 3 weeks ago, which resolved spontaneously and was attributed to a minor anal fissure. He has had no fever, vomiting, diarrhea, constipation, epistaxis, or easy bruising. He was born full-term via uncomplicated vaginal delivery and has met all developmental milestones. He takes no medications and has no known allergies. Family history is negative for bleeding disorders, inflammatory bowel disease, or gastrointestinal polyps.

On arrival, he is alert, sitting quietly in his mother’s lap, and appears mildly pale. He is afebrile with a temperature of 37.1 °C (98.8 °F). His heart rate is 132 bpm, blood pressure is 90/56 mmHg, respiratory rate is 26/min, and oxygen saturation is 99% on room air.