A technique for the preparation of Tc-99m red blood cells for evaluation of gastrointestinal hemorrhage.

Tc-99m labeled red blood cell (RBC) preparations are gaining wide acceptance in the diagnosis and localization of gastrointestinal bleeding. A major requirement of the radiopharmaceutical is that the percentage of Tc-99m attached to red cells in the injected dose must be extremely high, since free pertechnetate is secreted into the gastrointestinal tract and may obscure a bleeding site. We have developed a combined in vivo/in vitro labeling procedure which is simple and rapid, and which enables the administration of substantial amounts of RBC-bound Tc-99m and minimizes the amount of unbound technetium present. The technique is readily utilizable in any nuclear medicine clinic and requires no investigative pharmaceuticals.