BACKGROUND:There exists only very few data on in vitro and in vivo effects of gamma irradiation of red blood cells (RBCs) that have been leukoreduced by filtration before a subsequent irradiation. Reported studies reflect neither the current Food and Drug Administration (FDA) nor the European recommendations on timing of irradiation and subsequent storage. STUDY DESIGN AND METHODS:We studied 40 RBC units that were prepared from inline filtered whole blood and 40 RBC units that were filtered after component separation. All RBCs were stored in the additive solution saline-adenine-glucose-mannitol and leukoreduced on the collection day. In both groups, 20 components were irradiated on Day +14 with 30 Gy, and 20 served as nonirradiated controls. In vitro evaluation of both irradiated and nonirradiated RBC units was performed before and after irradiation on Days +1, +7, +14, +21, +28, +35, and +42 from the collection day. RESULTS: Gamma irradiation induced enhanced leakage of potassium ions and lactate dehydrogenase and an enhanced in vitro hemolysis rate in the irradiated components. However, in vitro hemolysis rate of both nonirradiated and irradiated components was remarkably lower than 0.8 percent, and the preservation of adenosine triphosphate over 42 days was satisfying. CONCLUSIONS: This study reflects the current FDA and European recommendations on timing of irradiation and subsequent storage. Our findings together with recent results of other investigations on the effect of gamma irradiation on leukoreduced RBCs allow the proposal that a storage time up to 28 days after irradiation is allowable.