This study was performed in single tertiary teaching hospital ED. We have retrospectively identified all adult patients who have received GIH protocol CT angiography during 2 years. Patients with trauma or without further diagnostic workup were excluded. The results of CT angiography was considered as positive if there was any signs of active extravasations of contrast materials, enhancement of the bowel wall, presence of vascular abnormalities, polyp, or tumor. The reference standard consisted of esophagogastroduodenoscopy, colonoscopy, sigmoidoscopy, angiography, bleeding scan, capsule endoscopy and surgery, either alone or in combination. Clinical severity was stratified according to the amount of transfused RBC during first 2 days. Patients were categorized into mild (1st quartile), moderate (2nd and 3rd quartile), and severe group (4th quartile). Diagnostic performance was measure by sensitivity, specificity, area under receiver operating characteristics curve (AUC), positive predictive value (PPV), and negative predictive value (NPV).