The quantity of T-lymphocytes in blood components has a bearing on transfusion-associated graft-versus-host disease. In 2001, leukocyte reduction was introduced as standard in blood component production in Norway. The requirement is < 106 residual leukocytes per unit, and the risk of transfusion-associated graft-versus-host disease is therefore substantially reduced (6). However, leukocyte reduction is not sufficient, as the condition has also been reported after transfusion with leukocyte-reduced blood components (7).
We see that several patient populations are not mentioned in the Norwegian guidelines, and therefore propose harmonisation with the more detailed international guidelines
Effective prevention of transfusion-associated graft-versus-host disease is achieved by irradiating blood components with doses of ionising radiation (25–50 Gy). This inhibits lymphocyte proliferation, while maintaining the viability and thus the clinical efficacy of erythrocytes and platelets. After irradiation of erythrocyte concentrates, however, potassium leakage from the erythrocytes increases gradually, leading to a rise in potassium in the additive solution (8). Furthermore, haemolysis increases in irradiated erythrocyte concentrates (9). To limit haemolysis and restrict the potassium content, the storage time for irradiated erythrocyte concentrates is shortened from the normal 35 days to 28 days after collection.
For exchange or intrauterine transfusions, however, erythrocyte concentrates must be used within 24 hours following irradiation, because fetuses and neonates are more vulnerable to severe hyperkalaemia.
Platelet concentrates can be stored for up to seven days, and can be irradiated throughout the storage period (9). Their shelf life is not shortened, as irradiation does not affect platelet function. The condition can also be effectively prevented by using a pathogen reduction method (10), whereby both lymphocytes and any microbial agents are deactivated through irreversible nucleic acid damage. Octaplasma and plasma products do not contain cells and do not require irradiation.
Viable T-lymphocytes persist in blood components for up to two weeks (11). Thus, the fresher the blood, the higher the risk of transfusion-associated graft-versus-host disease. Irradiation of fresh blood components is therefore particularly important.
Not all hospitals have an irradiator, and procuring irradiated blood components from a tertiary blood bank can be a logistical challenge. It is important that essential transfusion treatment is not delayed. If irradiated blood components cannot be procured, efforts should be made to give blood that is over 14 days old, to prevent the transfer of viable T-lymphocytes.