What is the process of pre-storage leucodepletion (white blood cell removal) for blood products?

Pre-Storage Leucodepletion Process for Blood Products

Pre-storage leucodepletion is performed by removing white blood cells from whole blood or blood components immediately after collection and before storage, typically using specialized filtration systems that are integrated into blood collection bags.

Methods of Leucodepletion

• Pre-storage leucodepletion is the standard practice in many countries, including the United States, as it provides more consistent quality control compared to bedside filtration 1
• The process involves filtering whole blood through specialized leukocyte reduction filters either immediately after collection or within hours of collection 2
• Two main approaches exist:
  • Filtering whole blood before component separation (in-line filtration) 3
  • Filtering individual blood components after separation (component-specific filtration) 1

Technical Process

• Blood is collected into specialized blood bag systems that incorporate integral leukocyte filters 4
• For whole blood filtration:
  • Blood is collected into a "bottom and top" (BAT) system with an integrated filter 4
  • The blood is held for 4-6 hours at room temperature or 12-18 hours at 4°C before filtration 4
  • The blood passes through the filter by gravity or gentle pressure 3
• After filtration, the leucodepleted blood can be separated into components (red cells, plasma, platelets) 3
• The entire process should be performed under controlled conditions according to validated methods meeting Good Manufacturing Practice (GMP) standards 5

Efficiency and Quality Control

• Effective pre-storage leucodepletion removes >99.9% of white blood cells (>3 log reduction) 4
• Quality standards typically require:
  • Less than 1 × 10^6 leukocytes per unit of blood product 3, 4
  • Minimal red cell loss (typically <10%) 4
  • Maintenance of appropriate hemoglobin content (46-76 g/unit) and hematocrit (54-62%) 4
• The filtration process may result in some platelet loss (up to 25-35%) which should be accounted for in transfusion planning 1

Benefits of Pre-Storage vs. Bedside Leucodepletion

• Pre-storage leucodepletion offers several advantages over bedside filtration:
  • Prevents accumulation of cytokines released by leukocytes during storage 6
  • Reduces storage lesions in red blood cells 7
  • Provides more consistent leukocyte removal 1
  • Eliminates the need for bedside filtration equipment and training 2
  • Reduces the risk of filtration errors at the bedside 2

Clinical Applications

• Pre-storage leucodepletion is particularly important for:
  • Patients requiring long-term transfusion support 2
  • Patients with acute myeloid leukemia receiving induction chemotherapy 1
  • Transplant recipients to prevent alloimmunization 8
  • Prevention of febrile non-hemolytic transfusion reactions 2
  • Reduction in transfusion-associated cytomegalovirus infections 2

Common Pitfalls and Considerations

• Variables that can affect filtration efficiency include:
  • Filter material, composition, and surface charge 5
  • Blood component composition and age 5
  • Temperature and flow rate during filtration 5
• Pre-storage leucodepletion has made additional filtration at the bedside unnecessary when using allogeneic blood products 2
• For cell salvage procedures, a 40-μm filter may still be indicated if small bone fragments contaminate the surgical field 2
• When administering platelets, it's important to use a clean giving set, as one previously used for red cells may cause platelets to adhere to residual red cells, reducing transfusion efficacy 2