Technical Considerations of Tc-99m Labeled Red Blood Cell Scans in the Detection and Localization of Gastrointestinal Bleeding Sites

Arteriography to detect gastrointestinal bleeding, which is often intennittent, is only likely to yield diagnostically useful infonnation if the patient is actively bleeding at a rate of greater than 1.0 cclmin at the time of the procedure. To avoid the unnecessary morbidity of a negative arteriogram we studied Tc-99m in vitro labeled red blood cell (RBC) scintigraphy as a screening test for arteriography on 111 patients. Fifty-seven of Ill patients (51%) had RBC scans consistent with active gastrointestinal bleeding. Twenty-three of these patients (40%) with positive scans had arteriography. Twelve of these 23 arteriograms (52%) were positive. Arteriograms were performed in 12 of the 54 patients with a negative scan. One of the 12 arteriograms was positive for active bleeding in the rectum. In retrospect, the scan was also positive but rectal activity was initially confused with bladder activity. Red blood cell scans are a reliable screening test for arteriography and they provide useful localizing infonnation in patients with negative arteriograms. Technical factors that will affect the results include (1) obtaining high labeling efficiency by using in vitro labeled red blood cells; (2) frequent acquisition of images over a 24-hr time period; (3) acquisition of dynamic images to localize confusing patterns of activity; and (4) acquisition of images to separate rectal and bladder activity.