Detection and localization of gastrointestinal bleeding using Tc-99m-pyrophosphate in vivo labeled red blood cells.

Eighteen patients with either clinically or laboratory-detectable gastrointestinal bleeding were studied using Tc-99m-PYP in vivo labeled red blood cells. In those patients with massive gastrointestinal bleeding, the site of bleeding was usually detected within the first half-hour of scanning. Slower bleeding required longer scanning time. In several patients, bleeding sites were detected which could not be located by other means. It was experimentally determined that as little as 5 ml of ingested whole blood labeled in vivo with Tc-99m-PYP could be detected in the upper gastrointestinal tract.