Irradiated blood refers to blood products that have undergone a specialized treatment with radiation. This process modifies the blood in a way that prevents a specific, rare but severe complication that can occur after a blood transfusion. This treatment does not make the blood radioactive, nor does it significantly alter the function of its essential components.
Purpose of Blood Irradiation
The primary reason for irradiating blood is to prevent a serious condition called Transfusion-Associated Graft-Versus-Host Disease (TA-GVHD). This rare complication happens when certain white blood cells, specifically T-lymphocytes, from the transfused donor blood recognize the recipient’s body as foreign. If the recipient’s immune system is weakened or unable to eliminate these donor T-cells, the cells can engraft and attack the recipient’s tissues and organs.
TA-GVHD can affect the skin, liver, gastrointestinal tract, and bone marrow, often leading to severe illness and, in most cases, is fatal. While rare, with fewer than one per million transfusions resulting in TA-GVHD, its high fatality rate makes prevention important. Irradiating blood inactivates these donor T-lymphocytes, rendering them unable to multiply and launch an immune attack.
How Blood Is Irradiated
Blood irradiation involves exposing cellular blood products to a controlled dose of ionizing radiation. This process uses either gamma rays, often from sources like cesium-137, or X-rays. Modern blood banks and hospitals increasingly use X-ray irradiators due to their operational advantages.
During the process, blood bags are placed within a specialized irradiator. The radiation dose is carefully measured to ensure that lymphocytes receive enough energy to be inactivated, 25 Gray (Gy) to the central part of the blood product. This dose is sufficient to prevent the T-cells from dividing, while causing minimal damage to other blood components like red blood cells, platelets, and plasma proteins.
Patients Who Need Irradiated Blood
Certain patient groups require irradiated blood due to their increased risk of developing TA-GVHD. Immunocompromised patients are a primary group, including those undergoing intensive chemotherapy, especially with drugs like purine analogues or alemtuzumab. Patients who have received or are about to receive bone marrow or hematopoietic stem cell transplants, whether from a donor or their own cells, also need irradiated blood. Individuals with certain congenital immune system disorders or conditions like Hodgkin’s disease are also at risk.
Premature infants and neonates, particularly those who have received intrauterine transfusions or require exchange transfusions, represent another vulnerable population. Additionally, recipients of directed donations from blood relatives, such as a parent or sibling, receive irradiated blood. This is because blood relatives share more genetic similarities, which can make the donor’s T-cells less likely to be recognized and eliminated by the recipient’s immune system.
Safety and Characteristics of Irradiated Blood
A common concern regarding irradiated blood is whether it becomes radioactive. The radiation treatment does not make the blood radioactive, and it poses no radiation risk to the patient or others. The process is similar to how airport scanners use X-rays on luggage, without making the luggage radioactive.
The radiation specifically targets and inactivates lymphocytes, leaving other components largely unharmed. Red blood cells, platelets, and plasma maintain their function and safety for transfusion. While irradiated red blood cells may have a slightly shorter shelf life, this does not compromise their effectiveness or safety within that period. Irradiated platelets, however, retain their normal shelf life.