Blood irradiation is a specialized treatment applied to blood products before transfusion. This process exposes cellular blood components, such as red blood cells, platelets, and granulocytes, to a controlled dose of radiation. Its primary purpose is to enhance the safety of blood transfusions for vulnerable individuals by preventing a rare but serious complication.
Why Blood Irradiation is Necessary
Blood irradiation prevents a severe complication known as Transfusion-Associated Graft-Versus-Host Disease (TA-GVHD). This condition occurs when viable T-lymphocytes in transfused blood recognize the recipient’s tissues as foreign. These donor T-lymphocytes can then engraft and attack the recipient’s own cells, particularly in individuals whose immune systems are unable to reject them.
TA-GVHD is rare but carries a high fatality rate, often exceeding 90%. Symptoms include fever, skin rash, liver dysfunction, and bone marrow suppression, typically appearing days to weeks after a transfusion. Irradiating the blood effectively inactivates these donor T-lymphocytes by damaging their DNA, preventing them from dividing and causing harm, while leaving other beneficial blood components functional. This targeted inactivation is currently the only effective method to prevent TA-GVHD.
Patient Groups Requiring Irradiated Blood
Certain patient populations are at an increased risk of developing TA-GVHD and therefore require irradiated blood products. Individuals with weakened immune systems are particularly susceptible, as their bodies may not effectively eliminate donor T-lymphocytes. This includes patients undergoing cancer treatment, such as those with Hodgkin lymphoma or leukemia, and individuals receiving intensive chemotherapy or radiation therapy.
Recipients of hematopoietic stem cell transplants (autologous or allogeneic) routinely receive irradiated blood because their immune systems are recovering or suppressed to prevent rejection. Patients with congenital immunodeficiency syndromes, such as severe combined immunodeficiency (SCID) or DiGeorge syndrome, also require irradiated blood due to their T-lymphocyte deficiencies.
Premature infants, especially those with very low birth weight, need irradiated blood, as their developing immune systems cannot fully reject foreign cells. All cellular blood components for intrauterine transfusions must also be irradiated. Transfusions from first-degree blood relatives also necessitate irradiated blood due to the higher likelihood of shared human leukocyte antigen (HLA) types, which can allow donor lymphocytes to escape detection.
How Irradiated Blood is Prepared
Blood irradiation is a controlled process performed in blood banks or hospital transfusion services. It involves exposing cellular blood components to a specific dose of ionizing radiation, either gamma rays (from Cesium-137 or Cobalt-60) or X-rays. Both methods are equally effective in preventing TA-GVHD.
A standard minimum radiation dose of 25 Gy (Gray) is applied to the blood product, with no part receiving more than 50 Gy. This dose is sufficient to damage the DNA of T-lymphocytes, preventing their proliferation, while causing minimal harm to other blood components like red blood cells and platelets. Irradiated blood does not become radioactive and poses no radiation risk to the recipient or those around them. Radiosensitive indicator labels are often applied to blood units to confirm that irradiation has been successfully performed.
Important Considerations for Recipients
For patients who may require irradiated blood, understanding the process and communicating with healthcare providers is important. While recommended for specific patient groups, it is not universally necessary for all transfusions. Patients at risk for TA-GVHD should ensure their medical team is aware of their need for irradiated blood, as it often requires a special order from the blood bank.
Irradiated blood is generally safe and effective, with radiation primarily inactivating T-lymphocytes without significantly affecting other blood components. The shelf life of irradiated red blood cells may be slightly reduced, typically to 28 days from the date of irradiation or the original expiry date, whichever comes first. In emergency situations, the medical team will weigh the immediate need for blood against the time required to prepare irradiated products, prioritizing rapid transfusion if necessary.