Explanatory note from IBTS
Why is blood irradiated?
Some recipients of blood transfusion have severe impairment of the immune system. These may include patients with congenital disorders of immunity, very premature babies or babies who get in utero transfusions, patients with some types of cancer, especially lymphomas or leukaemias, and patients receiving some drug treatments.
A particular type of immune cell in the transfused blood may cause these patients to develop a reaction to the transfusion, called transfusion-associated graft-versus- host disease. This reaction is almost invariably fatal.
Transfusion-associated graft-versus-host disease can be effectively prevented by irradiating the blood donation before it is transfused. This is done at the blood centres using a specially designed irradiation unit.
Over-irradiation
Excessive irradiation causes damage to the red cells, and causes them to leak potassium from inside the cells into the surrounding fluid. This happens anyway when blood is stored - irradiation speeds up the process.
The excess potassium can cause metabolic disorders in some patients, essentially leading to abnormal heart rhythms on rare occasions.
Under-irradiation
Under-irradiation may prevent eradication of the donor's immune cells and allow transfusion-associated graft-versus-host disease to develop in the patient receiving the transfusion.