Gastrointestinal (GI) blood loss scan is a nuclear medicine study that assists in detecting and localizing active GI tract bleeding (2 or 3 mL/min) for the purpose of better directing endoscopic or angiographic studies. This procedure can detect bleeding if the rate is greater than 0.5 mL/min, but it is not specific for site localization or cause of bleeding. Endoscopy is the procedure of choice for diagnosing upper GI bleeding. After injection of technetium-99m-labeled red blood cells, immediate and delayed images of various views of the abdomen are obtained. The radionuclide remains in the circulation long enough to extravasate and accumulate within the bowel lumen at the site of active bleeding. This procedure is valuable for the detection and localization of recent non-GI intra-abdominal hemorrhage. Images may be taken over an extended period to show intermittent bleeding.