Leukodepletion: White Blood Cell Removal in Blood Transfusions

Leukodepletion (leukoreduction) is the filtration of blood components to remove >99.9% of white blood cells (WBCs), reducing residual WBCs to <5 × 10⁶ per unit. It is standard practice in many countries for all cellular blood products.

Why Remove WBCs?

Donor WBCs in transfused components can cause:

• Febrile non-hemolytic transfusion reactions (FNHTR): Cytokines (IL-1, IL-6, TNF-α) from donor WBCs → fever, chills, rigors.
• HLA alloimmunization: Recipient forms anti-HLA antibodies → platelet refractoriness, delayed hemolytic reactions, graft-versus-host disease (GVHD) risk.
• Transfusion-associated GVHD (TA-GVHD): Viable donor T-cells engraft in immunocompromised host → fatal pancytopenia. Leukodepletion reduces but does not eliminate TA-GVHD risk; irradiation (25 Gy) is required for at-risk recipients.
• CMV transmission: Latent CMV in donor leukocytes. Leukodepletion (residual <5 × 10⁶ WBCs) is equivalent to CMV-seronegative blood for preventing transfusion-transmitted CMV in most guidelines.
• Immunomodulation (TRIM): Allogeneic WBCs may suppress recipient immunity → increased infection/recurrence risk (controversial).

How It's Done

• Prestorage leukodepletion: Filtration at blood center within 48 hrs of collection (preferred; reduces cytokine accumulation during storage).
• Bedside filtration: Inline filter during transfusion (less common now).
• Filters: porous media (polyester, polyurethane) or depth filters; trap WBCs by size/adhesion; allow RBCs/platelets to pass.

Indications (Universal in Many Jurisdictions)

• All cellular components (RBCs, platelets, granulocytes) for all patients (universal leukodepletion: UK, Canada, Europe, Australia, etc.).
• US: Strongly recommended for all; required for specific indications (prior FNHTR, HLA-alloimmunized, intrauterine/neonatal, potential transplant candidates, immunocompromised).

Quality Standards

• Residual WBCs <5 × 10⁶ per unit (≥3 log reduction).
• RBC recovery >85%; platelet recovery >70% (for platelet components).
• No significant hemolysis or platelet activation.

Leukodepletion is a cornerstone of modern transfusion safety, reducing infectious, immunologic, and inflammatory risks at modest cost.