Upper tract source
Esophagus/stomach
	Reflux esophagitis*
	Erosive gastritis/ulceration*
	Varices
	Cameron's erosions within a hiatal hernia
	Dieulafoy's lesion (i.e., dilated aberrant vessel underlying a small mucosal defect)
		Gastric antral vascular ectasia (i.e., “watermelon stomach”)
	Portal gastropathy
Small intestine
	Duodenitis
	Celiac sprue
	Meckel's diverticulum
	Crohn's disease (can occur anywhere but commonly involves terminal ileum)
Lower tract source
Colon
	Diverticula (usually causes overt bleeding)
	Ischemic colitis
	Ulcerative colitis
	Other colitis
	Infection (e.g., hookworm, whipworm, Strongyloides, ascariasis, tuberculous enterocolitis, amebiasis, cytomegalovirus)
Rectum
	Fissure
	Hemorrhoids
Any gastrointestinal source
Vascular ectasia/angiodysplasia
Carcinoma (especially colon)*
Vasculitis
Aortoenteric fistula
Other cancers (e.g., Kaposi's sarcoma, lymphoma, leiomyoma, leiomyosarcoa, carcinoid tumors, melanoma)
Large polyps
Telangiectasia (i.e., Osler-Weber-Rendu syndrome)
Blue rubber bleb nevus syndrome
Amyloidosis
Hemangioma
Radiation-induced mucosal injury
Extraintestinal source
Hemobilia
Hemosuccus pancreaticus
Hemoptysis
Nasopharyngeal (e.g., epistaxis, bleeding gums)
Factitious
Long-distance running
No source found