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Blood Bank

Irradiated Components

This section covers Irradiated Blood Components, a critical modification performed to prevent a rare but devastating complication of transfusion: Transfusion-Associated Graft-versus-Host Disease (TA-GVHD)

What is Irradiation of Blood Components?

  • Definition: The process of exposing cellular blood components (Red Blood Cells, Platelets, Granulocytes, Whole Blood) to a measured dose of ionizing radiation (gamma rays or X-rays) before transfusion
  • Mechanism: The radiation damages the DNA of donor T-lymphocytes present within the blood component. This renders these lymphocytes incapable of proliferating (dividing and multiplying) after being transfused into the recipient
  • Goal: To prevent viable donor T-lymphocytes from engrafting in the recipient, multiplying, and attacking the recipient’s tissues (TA-GVHD)
  • Important Distinction: Irradiation does NOT sterilize the blood product; it does not kill bacteria, viruses, or parasites. Its sole purpose is to inactivate donor T-lymphocytes

Why Irradiate? The Threat of TA-GVHD

  • Transfusion-Associated Graft-versus-Host Disease (TA-GVHD): This is a rare but usually fatal complication of transfusion
    • Pathophysiology: It occurs when viable donor T-lymphocytes are transfused into a recipient who cannot recognize or eliminate them. These donor lymphocytes engraft, proliferate, and mount an immune attack against the recipient’s “foreign” tissues (skin, liver, gut, bone marrow)
    • Risk Factors: TA-GVHD is more likely when:
      1. The recipient is significantly immunocompromised (e.g., congenital immunodeficiencies, hematopoietic stem cell transplant recipients, patients receiving intense chemotherapy/immunosuppression)
      2. The donor and recipient share HLA haplotypes (genetic markers for the immune system), making it harder for the recipient’s immune system to recognize the donor lymphocytes as foreign. This is particularly relevant in directed donations from blood relatives (parents, siblings, children)
  • Prevention: Since TA-GVHD is difficult to treat and often fatal, prevention through irradiation of cellular components for at-risk recipients is the standard of care

Indications for Irradiation (Who Needs Irradiated Blood?)

Irradiation is indicated for patients whose immune systems may be unable to eliminate transfused donor lymphocytes or when there’s an increased risk of shared HLA types:

  • Severely Immunocompromised Patients
    • Congenital immunodeficiency syndromes (e.g., SCID)
    • Hematopoietic Progenitor Cell (HPC) / Stem Cell Transplant recipients (both autologous and allogeneic)
    • Patients receiving intense immunosuppressive therapy (e.g., certain chemotherapy regimens, anti-thymocyte globulin)
    • Patients with Hodgkin lymphoma
  • Fetal and Neonatal Transfusions
    • Intrauterine transfusions
    • Neonatal exchange transfusions
    • Premature infants (especially low birth weight) - policies vary, but often irradiated
  • Directed Donations from Blood Relatives: Mandatory for first- or second-degree relatives due to the increased likelihood of shared HLA haplotypes
  • HLA-Matched Components: If components (especially platelets) are specifically selected to be HLA-matched for a recipient, irradiation is required because the recipient’s immune system may not recognize the donor lymphocytes as foreign
  • Granulocyte Transfusions: Mandatory due to the high number of viable lymphocytes present

Note Policies may vary slightly between institutions, but these represent the core indications

The Irradiation Process

  • Equipment: Performed using a dedicated blood irradiator. These devices contain either:
    • A radioactive source (commonly Cesium-137 or Cobalt-60) emitting gamma rays
    • An X-ray generating system
  • Dose: The standard required dose is:
    • 25 Gray (Gy): delivered to the central portion of the unit
    • A minimum dose of 15 Gy delivered to any other part of the unit
  • Verification: An irradiation indicator label is usually affixed to the unit before irradiation. This label undergoes a visible color change upon exposure to the required radiation dose, providing visual confirmation that the process was performed

Which Components Are Irradiated?

Irradiation is necessary only for components containing significant numbers of viable T-lymphocytes:

  • Red Blood Cells (RBCs)
  • Platelets: (Whole Blood Derived and Apheresis)
  • Granulocytes: (Mandatory for all units)
  • Whole Blood

Components NOT Requiring Irradiation

These components are essentially acellular or contain non-viable lymphocytes:

  • Fresh Frozen Plasma (FFP)
  • Plasma Frozen within 24 hours (PF24)
  • Cryoprecipitated AHF
  • Cryoprecipitate-Reduced Plasma
  • Plasma Fractionation Products (Albumin, IVIG, Factor Concentrates)

Impact of Irradiation on Components (Especially RBCs)

While necessary for safety, irradiation does have effects, particularly on Red Blood Cells:

  • RBC Membrane Damage: The radiation causes some damage to the RBC membrane
  • Increased Potassium Leakage: This membrane damage leads to an accelerated rate of potassium (K+) leaking from the RBCs into the supernatant plasma/additive solution
  • Potentially Reduced Viability: May slightly decrease the 24-hour post-transfusion survival of RBCs, though usually still well above the acceptable minimum
  • Impact on Expiration Date (CRITICAL): Due to the increased potassium leak and potential impact on viability, the expiration date of irradiated Red Blood Cells is changed:
    • The unit expires on the original expiration date OR 28 days from the date of irradiation, WHICHEVER COMES FIRST
    • Example 1: An RBC unit with a 42-day original expiry is irradiated on Day 10. Its new expiry date is Day 10 + 28 days = Day 38 (sooner than the original Day 42)
    • Example 2: An RBC unit with a 42-day original expiry is irradiated on Day 30. Its new expiry date is Day 30 + 28 days = Day 58, BUT the original expiry is Day 42. So, the unit expires on Day 42 (whichever is sooner)
  • Platelets: Irradiation has minimal impact on platelet function or storage. The original 5-day (or 7-day) expiration date is retained for irradiated platelets

Storage and Expiration (Post-Irradiation)

  • RBCs: Store at 1-6°C. Expiry is original date OR 28 days post-irradiation, whichever is sooner. Must check the label carefully!
  • Platelets: Store at 20-24°C with agitation. Original 5- or 7-day expiry applies
  • Granulocytes: Store at 20-24°C without agitation. Original 24-hour expiry applies

Administration

  • No special administration procedures are required specifically because a unit is irradiated
  • Standard procedures apply: ABO/Rh compatibility, crossmatch (for RBCs/Granulocytes), standard blood filter, infusion within 4 hours

Key Terms

  • Irradiation: Treatment with ionizing radiation (gamma or X-rays)
  • TA-GVHD (Transfusion-Associated Graft-versus-Host Disease): Complication where donor T-lymphocytes attack recipient tissues
  • T-Lymphocyte: Type of white blood cell responsible for cell-mediated immunity; inactivated by irradiation
  • Immunocompromised: Having a weakened immune system
  • HLA (Human Leukocyte Antigen): Immune system markers on cells; shared haplotypes increase TA-GVHD risk in related donors
  • Gray (Gy): Unit of absorbed radiation dose
  • Blood Irradiator: Device used to irradiate blood components
  • Irradiation Indicator: Label that changes color to visually confirm irradiation