Clinical value of in vitro labeling of red blood cells with technetium 99m-scintigraphy in the detection of acute gastrointestinal bleeding

We evaluate the clinical value of in vitro labeling of red blood cells with technetium 99m (99mTc-RBC) scintigraphy for the detection of gastrointestinal (GI) bleeding sites. Ten patients referred with clinical evidence of GI bleeding and negative colonoscopy underwent 99mTc-RBC scintigraphy after endovenous administration of 925 MBq (25 mCi) 99mTc-RBC labeled by a simple technique, previously described by ourselves. Dynamic images of the abdomen were taken at 10 s intervals for 40 min. Then, 5 min images were obtained 1, 3 and 5 hours after cell administration. Delayed images up to 24 hours were obtained when early results were negative. All the patients with suspected GI bleeding were confirmed to have active hemorrhage up to 24 hours. The identification of bleeding sites was 40% (40 min), 20% (60 min) and 30% up to 24 hours. Of the nine patients with definite active hemorrhage, the bleeding sites were identified by surgery in all of them; and in the remaining patient, without active hemorrhage, the bleeding site was not identified by surgery. In conclusion, the simplicity, reproducibility and reliability of this technique of in vitro labeling of red blood cells, particularly when bleeding rates are low and intermittent, make it, in our point of view, the first line of investigation in any patient with suspected bleeding from the colon or upper GI tract if endoscopic evaluation is not possible in the latter.