Abstract
Red Blood Cell (RBC) alloimmunization is a result of the adaptive immune response to foreign antigen(s) encountered through exposure to RBC’s from a genetically different member of the same species. It is a common complication of blood transfusion occurring in 1-3% of transfused patients. Alloantibodies are detected using a test called the indirect antiglobulin test (IAT) or antibody screen categorized as warm or cold -reacting. The clinical significance of warm alloantibody production is that they react at 37°C and cause hemolysis in the fetus and newborn as well as hemolytic transfusion reactions in the transfused patient. Approximately 36,000 units of packed RBC’s are transfused every day in the United States, and with between 4.5 and 5 million Americans receiving blood transfusions each year, there is substantial opportunity for alloimmunization. Routine compatibility testing methods are employed to ensure that compatible red blood cells are transfused. ABO, and Rh screening is performed and the detection of clinically significant non-ABO alloantibodies is reliant on an antibody screen or IAT. A positive antibody screen will elicit further testing to identify the antibody specificity. Once the antibody is identified, donor RBC’s phenotypically negative for the cognate antibody(ies) is/are serologically crossmatched using an antiglobulin reagent to, commonly referred to as the Anti-Human Globulin (AHG) crossmatch. Autoimmune hemolytic anemia develops due to development of an autoantibody against autologous RBC’s, as well as clinical or laboratory evidence of hemolysis. The direct antiglobulin test is used to determine the presence of RBC membrane bound immunoglobulin G and/or complement. Recently, Nixon and colleagues concluded that the AHG crossmatch has a high failure rate due to recipient antibody titer and zygosity of donor cells and is not reliable in detecting incompatibility related to minor blood group antigens. In fact, when samples containing well characterized alloantibodies were intentionally crossmatched against donor RBC’s phenotypically positive for the antigen, the results showed compatible crossmatches in 89 out of 240 (37%).11 In other words, if these units were used for transfusion, 37% of the patients would have received incompatible red blood cells, despite the compatible crossmatch. Fifty four previously frozen plasma samples from patients with clearly identified alloantibodies using serologic technique were obtained and flow cytometry test method was compared to the predicate crossmatch and titer serology tests. Based on the data presented, descriptive statistics and statistical analysis, I conclude that the use of flow cytometry is essentially equivalent to the predicate, routine methods currently utilized in routine Transfusion Medicine. Additionally, flow cytometry techniques in the identification of autoantibody may provide adjunct information regarding the specificity, and reactivity of the antibody.