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Gastrointestinal bleeding scan (GIBS) is a non-invasive diagnostic radionuclide imaging study to evaluate patients with a suspected overt GI bleed, especially involving mid and lower gastrointestinal (GI) tract. It is performed with 99mTc-RBCs and helps determine the bleeding status (active or intermittent), gross localization, and estimation of the amount.[1]  Gastrointestinal bleeding (GIB) can be occult, overt, or obscure. Occult GIB has a positive guaiac test or iron deficiency anemia with no visible signs of bleeding. Overt GIB has signs of active bleeding such as melena, hematemesis, or hematochezia. Obscure GIB has persistent or recurrent bleed with no known source of bleeding after negative bidirectional endoscopy. For purposes of geographical localization and potential intervention, GI bleeding typically classifies as upper, mid, and lower. Upper gastrointestinal bleed (UGIB) includes bleeding up to the level of the ampulla of Vater, which is within reach of esophagogastroscopy; this can identify major causes such as gastric and duodenal ulcers, esophageal varices, esophagitis, and gastritis. Mid GIB includes up to the level of the terminal ileum, which undergoes an evaluation with capsule endoscopy; this can diagnose etiologies such as Meckel diverticulum, angiodysplasia, and Crohn disease.[2] Most common causes of lower GIB within reach of colonoscopy are angiodysplasia, polyps, diverticulosis, inflammatory, and infectious colitis.  The clinical signs and symptoms of overt GI bleeding are often unreliable and can manifest late, especially if it is intermittent. Prompt and timely identification of GI bleed is essential for the next step in patient management, which includes CT angiography, Catheter angiography, surgical intervention, or observation.

Radionuclide GI bleeding scan is normally a safe procedure. The risk of the procedure is radiation exposure. Lactating patients who receive technetium labeled RBCs need a 12-hour interruption of breastfeeding.[8][1]