Irradiated blood is a blood product that has been treated with a measured dose of ionizing radiation, typically gamma rays or X-rays, before being transfused. This process is a standard safety measure performed by blood banks and transfusion services worldwide. The primary objective of this treatment is to prevent a rare but serious complication associated with blood transfusions. This modification process does not alter the beneficial components of the blood, such as red blood cells or platelets, but instead targets a very specific type of cell.
The Mechanism of Blood Irradiation
The need for blood irradiation stems from the risk of Transfusion-Associated Graft-versus-Host Disease (TA-GVHD), a condition that is often fatal. This disease is triggered by viable donor T-lymphocytes present in transfused blood products. These T-cells recognize the recipient’s tissues as foreign. If the recipient’s immune system cannot eliminate them, the donor cells can engraft, proliferate, and launch a widespread attack on the patient’s organs.
To neutralize this threat, cellular blood components like red cells and platelets are exposed to a minimum dose of radiation, usually 25 Gray (Gy). This precise dose is carefully calibrated to penetrate the blood product and damage the DNA of the T-lymphocytes. The DNA damage renders them incapable of dividing and multiplying, which is necessary for them to mount an immune response against the host.
T-lymphocytes are highly sensitive to radiation compared to the other components of the blood product. Red blood cells and platelets are largely unaffected at this specific radiation level. By inactivating the proliferative capacity of the T-cells, irradiation prevents the donor cells from establishing a self-sustaining population that could attack the recipient’s tissues. This effectively eliminates the risk of TA-GVHD and is the only universally accepted prevention method.
Patient Populations Requiring Irradiated Blood
Patients who require irradiated blood are generally those whose immune systems are severely compromised or those who receive blood posing a specific risk of containing donor T-cells. A major category includes patients undergoing hematopoietic stem cell transplantation (both allogeneic and autologous). These patients must receive irradiated products from the time of conditioning until their immune function recovers, which can be up to a year or longer.
Another high-risk group includes patients with congenital immunodeficiencies that specifically affect T-cell function, such as severe combined immunodeficiency (SCID). Individuals receiving certain potent chemotherapies or immunosuppressive agents, such as purine analogues or Alemtuzumab, also have significantly lowered immune defenses, making them susceptible to TA-GVHD. Irradiated blood is required during and for a specified period following this treatment.
Irradiation is also mandatory for certain transfusions given to very young patients, including cellular blood components used for intrauterine transfusions (IUT) and neonatal exchange transfusions (ET). Individuals with normal immune function must receive irradiated blood if the donation comes from a first- or second-degree blood relative. The genetic similarity in these cases increases the likelihood that the recipient’s immune system will not recognize the donor T-cells, allowing them to proliferate.
Practical Considerations for Irradiated Blood Products
A common concern among patients is whether the blood remains radioactive after treatment, but the answer is definitively no. The process uses gamma or X-ray radiation to treat the product, but the blood itself does not become radioactive and poses no radiation risk to the recipient or healthcare staff. The specialized equipment delivers a dose of energy to the cells, similar to an X-ray machine, and the unit is safe to handle once treatment stops.
While the T-cells are inactivated, the essential functions of the other blood components are largely maintained. Platelets and granulocytes retain their functional capabilities following irradiation. However, irradiation does have a measurable impact on the storage life of red blood cells (RBCs).
The radiation causes an accelerated leakage of potassium from the RBCs into the storage solution. This can be problematic for patients with impaired kidney function or for neonates.
Therefore, the maximum allowable shelf life for irradiated red blood cells is typically shortened to 28 days from the date of irradiation or the unit’s original expiration date, whichever comes first. For neonates and fetuses, units are often required to be transfused within 24 hours of irradiation to minimize the risk associated with elevated potassium levels.