Blood transfusions are critical for saving lives. Timely transfusion of blood replenishes blood lost during surgical procedures or due to serious injury. Several conditions, such as hemophilia, sickle-cell anemia or cancer can also result in patients needing blood transfusions. At a global level, approximately 120 million units of blood are collected through blood donations every year.1 The donated blood is processed and tested before it is used for transfusion. While blood transfusion is generally safe, there are some risks, such as the inadvertent transmission or activation of viruses or development of serious allergic reactions, associated with it. We have made great strides in understanding the basis of these risks and have found ways to circumnavigate them.
What types of transfusion reactions can jeopardize the safety of blood transfusions?
Transfusions are generally safe and there are more successful red blood cell (RBC) transfusions than those that produce severe adverse effects.2 However, blood transfusions can induce immunosuppression by eliciting antibodies for human leukocyte antigen (HLA) or transmit viruses such as cytomegalovirus (CMV). Transfusion reactions, such as febrile non-hemolytic transfusion reaction (FNHTR) or platelet transfusion refractoriness, can be induced by leukocyte (or white blood cell, WBC) antibodies.3 The presence of WBCs in blood and platelet products is associated with an increased incidence of FNHTR, transmission of CMV and alloimmunization to HLA antigens in transfusion recipients.3 Depletion of leukocytes below a specific level can prevent HLA alloimmunization.4 Removal of >99.9% of leukocytes in platelets and red cell units can also reduce potential transmission of CMV.5
What is leukoreduction and how is it performed?
Leukoreduction (or leucoreduction) entails intentionally reducing the number of leukocytes from RBCs and platelets obtained from whole blood fractions or after apheresis. Centrifugation or filtration can reduce approximately 99.995% of leukocytes.6 Buffy coat method and whole blood filtration method are two commonly used approaches for reducing the number of leukocytes. Leukoreduction can lower the WBC count to 5 x 106 per unit or below, thus minimizing complications associated with transfusions.7,8 For more than three decades now, leukoreduction has become standard practice and is universally adopted to reduce adverse reactions resulting from blood transfusions.9 Guidelines for enforcing universal leukoreduction have been published to mitigate the risks associated with transfused blood products in the U.S., Canada and Europe; in the U.S., a WBC count of 5 x 106 per unit or below is acceptable before transfusion.
Flow cytometric evaluation of residual leukocytes
Enumerating residual leukocytes in leukoreduced blood products is critical to ensure the quality of blood components. Establishing reliable quality control processes is also equally important. Several methods to evaluate the number of residual leukocytes in blood after leukoreduction are available. Flow cytometry and counting cells using the manual Nageotte chamber or using automated leukocyte counters are well-established methods. Flow cytometry is an effective and FDA-cleared counting method for evaluating leukoreduced blood products.7 Comparisons evaluating the performance of different methods used for residual leukocyte enumeration show that flow cytometry is superior in terms of accuracy compared to Nageotte hemocytometry.8 Flow cytometry is also validated for accuracy, precision, linearity and robustness counting.10
Interested in preparing for the IVDR? Visit our IVDR page to learn more about the measures you can take to prepare your lab.
