In vivo/in vitro labeling of red blood cells with 99mTc.

Red blood cells (RBC) were labeled with 99mTc in vitro after in vivo pretreatment with a stannous solution. The whole in vivo/in vitro procedure took 30-40 min. Pretinning was carried out by injection of either 6 mg DTPA and 0.6 mg Sn++ (Sn-DTPA) or 5 mg pyrophosphate and 0.7 mg Sn++ (Sn-PYP). The results of 1,356 patients were evaluated. The labeling yield was 89.7% (mean) after pretinning with Sn-DTPA and 88.2% following Sn-PYP pretreatment, the median values being 94% and 92%, respectively. The new method was successfully used in over 2,000 patients who had a radionuclide-ventriculography and in 38 patients studied for localization of occult gastrointestinal bleeding. Adverse side effects have never been observed.