Blood irradiation is a process where blood is exposed to a minimum of typically 25 Gy of radiation (Gray [Gy] is a unit of measurement for ionising radiation). Blood products are modified by it and radiation prevents lymphocytes from being able to reproduce whilst causing negligible damage to the blood cells.
“Ionising irradiation eliminates the functional and proliferative capacities of T cells, leaving other blood components, especially red blood cells, granulocytes and platelets, functional and viable. This is possible because T cells are more radiosensitive than other blood components.”2 “For immunosuppressed or immunocompetent patients potentially suffering from TA-GvHD after transfusion, it is vital that T cells are modified so that they cannot attack host tissues.”3
Blood products can be called “irradiated” in the US, once 25 Gy of irradiation is targeted at the centre, with the equipment calibrated to deliver no less than 15 Gy to any part of the canister. In Europe, a minimum of 25 Gy has to be applied to any part of the blood product in the irradiator. In order not to harm the other blood components, the maximum dose is generally defined as 50 Gy. All details on dosage can be found in Standards for Blood Banks and Transfusion Services, 32nd Edition by The American Association of Blood Banks (AABB) as well as in the Guidelines on the use of irradiated blood components issued by the British Society for Haematology in 2020.