What is Leukoreduction?

Leukoreduction, at its most basic, refers to the process of removing white blood cells (leukocytes) from blood products prior to transfusion. These cells, while a vital component of the immune system, can cause several complications when transfused from a donor to a recipient.

Why is Leukoreduction Done?

  1. Prevent Febrile Non-Hemolytic Transfusion Reactions (FNHTR): One of the most common reactions to transfusion is a fever caused by white blood cells in the transfused blood. By removing these cells, the chance of FNHTR is significantly reduced.

  2. CMV Transmission: Cytomegalovirus (CMV) is a common virus often carried silently in white blood cells. Transfusing leukoreduced blood reduces the risk of transmitting CMV, especially critical for immune-compromised recipients.

  3. Platelet Refractoriness: Over time, some patients can become refractory, or resistant, to platelet transfusions. This refractoriness often occurs due to antibodies formed against leukocytes. By using leukoreduced blood products, the incidence of this issue is decreased.

  4. Reduction of HLA Alloimmunization: The human leukocyte antigen (HLA) system is complex, and mismatches can lead to immune reactions. Leukoreduction decreases the risk of a patient developing these immune reactions.

How Does Leukoreduction Work?

The process usually involves passing the blood product through a filter specifically designed to capture white blood cells. These filters are highly efficient and can remove more than 99% of leukocytes from the blood product.

The Mechanics of Filtering

Leukoreduction filters are marvels of medical engineering. They are designed with specific pore sizes that allow smaller elements like red blood cells, platelets, and plasma to pass through while effectively capturing the larger leukocytes.

The Timing of Leukoreduction

There are generally two timeframes when leukoreduction can be performed:

  1. Pre-storage Leukoreduction: This method is performed soon after blood collection, often within hours. It's the preferred method for many blood banks because removing leukocytes early can prevent some of the issues associated with their breakdown over time.

  2. Bedside Leukoreduction: This is performed right before transfusion at the patient's bedside. While effective, it's less common than pre-storage leukoreduction because of the potential for logistical complications in a clinical setting.

Filter Materials and Design

The materials used in these filters are typically biocompatible to ensure there's no adverse reaction with the blood products. Some filters utilize polyester fibers, while others might use synthetic materials. The design of the filter ensures optimal flow rates, minimizing the time it takes to process each unit of blood.

Beyond Leukocytes: Additional Benefits

While the primary purpose is to remove leukocytes, the process also inadvertently reduces the presence of other potentially harmful substances. For instance, when leukocytes break down over time, they release cytokines which can cause febrile reactions in recipients. By reducing the leukocyte count, the amount of these substances is also significantly reduced.

Quality Control in Leukoreduction

Blood banks and transfusion services maintain strict quality control measures to ensure the efficiency of leukoreduction. Random units are periodically tested to verify that the leukocyte count is below the accepted threshold. This ensures that patients consistently receive blood products that meet the highest safety standards.

Who Needs Leukoreduced Blood Most?

While the benefits of leukoreduction are universal, certain patient populations derive particular benefit from leukoreduced products:

  1. Immuno-compromised Patients: Immuno-compromised patients have reduced defenses against foreign cells, including transfused leukocytes. Introducing non-leukoreduced blood can lead to adverse reactions or infections that their bodies might struggle to combat. Moreover, these patients are more susceptible to transfusion-related complications like Graft-Versus-Host Disease (GVHD), where donor white cells might attack the recipient's tissues. Leukoreduced blood minimizes these risks, providing a safer transfusion option.

  2. Neonates and Pediatrics: Neonates and pediatric patients have immature immune systems that might not effectively handle the potential challenges posed by transfused leukocytes. Using leukoreduced products for these groups reduces the risk of adverse reactions and supports their still-developing immune defenses.

  3. Chronic Transfusion Patients:Patients with conditions like sickle cell disease often require multiple transfusions throughout their lifetime. Each transfusion with non-leukoreduced blood increases the risk of sensitization, where the immune system becomes reactive to foreign leukocytes. Over time, this sensitization can lead to transfusion reactions, reduced efficacy of future transfusions, and other complications.

Leukoreduction as a Standard Practice

In modern transfusion medicine, leukoreduction has become standard practice in many regions worldwide. Recognizing the broad benefits of this process, many blood banks and collection centers have made the decision to leukoreduce all donated blood. In fact, a large number of hospital blood banks now maintain an inventory that is 100% leukoreduced, ensuring that all patients receive the safest blood products available.

This proactive approach simplifies inventory management for hospitals and ensures that high-risk patients always receive leukoreduced blood, even in emergency situations where there may not be time to make specific product selections.