GSTM1 and Hematochezia: The diagnosis of GIB was identified based on the clinical evidence of gross hemorrhage such as hematemesis, coffee-ground emesis, hematochezia, and/ormelena and/or supported by an assessment of nadir hemoglobin (Hb) during index hospitalization compared to baseline Hb and/or confirmed by diagnostic imaging such as computed tomography (CT), CT angiography, capsule endoscopy, tagged red blood cell scan, esophagogastroduodenoscopy (EGD), or colonoscopy.