Suggestion for cause of substandard radiolabeling of red blood cells using UltraTag.

To the Editor: The development and introduction of the UltraTag® kit (Mallinckrodt, Inc., St. Louis, MO) offered a substantial improvement in the ability to conveniently and efficiently radiolabel red blood cells with mTc (1 ). This particular cell-labeling technique is especially desirable for use in studies of gastrointestinal hemorrhage (GI bleed) since even minimal levels of free pertechnetate that might occur with other techniques potentially are interferential for image interpretation (2). Because a variety of factors can adversely affect radiolabeling procedures, radiochemical purity testing should be routinely performed before patient administration (3). A review of Ultra Tag's labeling procedures performed in this institution, since commercialization in 1991, revealed that 8 of 368 (2%) preparations were of substandard labeling efficiency (i.e., < 90% radiochemical purity). Preparation factors that were involved in each of these substandard products were evaluated, and are detailed on Table 1. None of these substandard products was administered to patients. In each instance a second UltraTag kit from the same lot was prepared successfully using pertechnetate from the same eluate vial (three instances) or pertechnetate from a fresh eluate (five instances). A substandard product resulting from adding syringe components in the wrong order is not unexpected due to the nature of the sequential L E TO T T THE E R S EDITOR