A leukocyte filter is a specialized medical device designed to remove white blood cells, also known as leukocytes, from donated blood products. This filtration is routinely performed before blood or its components are transfused. The primary goal is to enhance the safety of blood transfusions by reducing potential adverse reactions.
Why Leukocytes Are Filtered
Transfusing blood components containing leukocytes can lead to various complications in the recipient. One common issue is febrile non-hemolytic transfusion reactions (FNHTR), characterized by fever and chills. These reactions result from cytokines released by donor leukocytes.
Another concern is the transmission of leukocyte-borne viruses. Viruses like Cytomegalovirus (CMV), human T-cell lymphotropic virus (HTLV), and Epstein-Barr virus (EBV) can be transferred to the recipient during transfusion. Leukoreduction can significantly lower the risk of transmitting these infections.
Alloimmunization is also a risk, where the recipient develops antibodies against donor human leukocyte antigens (HLA). This can make it difficult to find compatible blood for future transfusions and may lead to platelet refractoriness, a condition where platelet transfusions become ineffective. In severe cases, transfusion-associated graft-versus-host disease (TA-GVHD) can occur, especially in immunocompromised patients. TA-GVHD involves transfused donor lymphocytes attacking the recipient’s tissues. Additionally, the presence of leukocytes can contribute to immunomodulation, potentially suppressing the recipient’s immune system.
How Leukocyte Filters Work
Leukocyte filters operate through a combination of physical and chemical mechanisms. The filter material, composed of synthetic microfibers (e.g., polyester or cellulose acetate), forms a non-woven web with precisely engineered pores. Pores are large enough for red blood cells and plasma to pass through, yet small enough to trap larger, less deformable white blood cells.
Beyond physical sieving, many filters also employ adsorption. The surface of the filter material is often modified with chemical characteristics or charges to attract leukocytes. This enhances the filter’s ability to capture white blood cells, including those smaller than the pore size.
These filters remove over 99.9% to 99.99% of leukocytes, reducing the count to less than 5 x 10^6 cells. Filtration occurs at two main stages: pre-storage leukoreduction (at collection centers shortly after donation) or bedside leukoreduction (immediately before transfusion). Pre-storage filtration is preferred as it prevents the accumulation of inflammatory cytokines during storage, preserving the blood product’s quality.
Applications and Patient Benefits
Leukocyte filters improve transfusion safety and benefit certain patient populations. Patients with recurrent febrile non-hemolytic transfusion reactions receive leukoreduced blood to prevent these episodes. For immunocompromised individuals, such as transplant recipients or those undergoing chemotherapy, leukoreduction is used to prevent the transmission of CMV and reduce the risk of TA-GVHD.
Neonates and infants also receive filtered blood due to their developing immune systems and higher susceptibility to complications. Patients requiring long-term transfusion support, such as those with sickle cell anemia or thalassemia, benefit from leukoreduction as it reduces the risk of alloimmunization, making future transfusions easier. The widespread use of leukocyte filters contributes to improved transfusion safety for a broader range of patients by reducing adverse events.