111In oxine labeled red cells for detection of simulated lower gastrointestinal bleeding in an animal model.

111In oxine in vitro labeled red cells were evaluated in rabbits for the ability to detect gastrointestinal (GI) bleeding. A mean labeling efficiency of 81% (+/- 15.5%) was achieved. Biodistribution and translocation data demonstrated 81% of the activity within the blood pool at four hours after intravenous injection, falling to 29% by 72 hours. Peak urine excretion occurred after 60-150 minutes. Normal GI excretion was less than 1% over 72 hours. Simulated lower GE bleeding was imaged at 4, 12, and 72 hours, and amounts as small as 2 ml (1% blood volume) were seen. In rabbits the total body dose of injected 111In is 0.15 mGy/MBq (0.56 rad/mCi), and the critical organ is the spleen which received 0.49 mGy/MBq (1.82 rad/mCi). 111In oxine labeled red cells provide a sustained blood pool label without significant accumulation in the GI tract, and may have a potential use in the detection of intermitent GI bleeding in humans.