الفهرس 
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Abstract
It is undeniable that RBC transfusions help to save lives in diverse acute situations and ameliorate suffering in chronic patients in condition that safe transfusion is applied. In multitransfused thalassaemic patients, haemagglutination fails to phenotype the patient’s blood group antigens due to the presence of donor-derived erythrocytes. DNA-based methods can overcome the limitations of haemagglutination and can be used to determine the correct antigen profile of these patients in order to avoid acute and delayed hemolytic transfusion reaction as well as alloimmunization which is mostly high in this group of patients. Once alloantibodies were developed, the management of thalassaemia patients will become more complicated. Our aim was to improve clinical and long term outcomes in thalassemic patients and to compare results of serological phenotyping and DNA-based red cell genotyping to develop an algorithm in order to identify which cases should proceed to molecular testing Our study was targeting thalassemic patients; the first group was newly diagnosed thalassemic patients, while second group was previously diagnosed thalassemic patients with history of blood transfusion Screening test was performed on second group to subdivide it to 2 subgroups; first with positive screening (alloimmunized), second with negative screening. Phenotyping and genotyping was performed on newly diagnosed patients and negative screening subgroup to analyze the difference between results of serological phenotyping and molecular genotyping in thalassemic patients and the effect of transfusion on their results over one year period Our results showed that the incidence of alloimmunization in our study was 6.3% and all of these RBCs alloantibodies are directed towards the Rh system and kell antigen. Regarding results of phenotyping and genotyping; there was no significant difference between results of the two methods when performed to type extended RBCs antigen profile for newly diagnosed patients. On the other hand there was superiority for genotyping over phenotyping when performed in previously diagnosed thalassemic with history of transfusion. Moreover, it was noticed that the percent of identity between results of the two methods was higher in newly diagnosed thalassemic patients, while percent of discrepancy is higher in previously diagnosed thalassemic patients with history of transfusion and that mixed field results was reported only with the previously diagnosed group. Although superiority of genotyping over phenotyping is clear and reported for chronically transfused patients, there is no superiority for genotyping over phenotyping when performed to determine extended blood group typing for patients with no history of previous transfusion. chronically transfused patients represent a special class of blood recipients as they are at higher risk of alloimmunization which is a major complication associated with repeated RBC transfusions. The main obstacle in alloimmunized patient is the restricted number of compatible units due to serologic incompatibility, makes the selection of appropriate antigen-negative RBC units for future transfusion difficult, espicially in a patient with rare and multiple alloantibodies, that delays the use of a transfusion therapy and presents the risk of haemolytic transfusion reaction Avoiding alloimmunization in patients on lifelong transfusion therapy should decrease the cost of treatment on the long run and improve the patients’ quality of life, as it will decrease number of transfusion requirements and time spent in the hospital. Avoidance or at least restriction of alloantibodies formation in those groups can be achieved by phenotyping for Rh and Kell system. There is no doubt that accurate RBC typing of patients and blood donors is essential to prevent alloimmunization and hemolytic transfusion reactions. Although the haemagglutination method is regarded as the gold standard in blood group identification, the results may be unreliable in certain situation. Red blood cell molecular-based genotyping can be helpful in determining the actual extended blood group systems in multiply transfused patient populations and assisting in the identification of suspected antibodies and the selection of antigen-negative RBCs for transfusion. Molecular testing is a rapidly advancing field that has been successfully implemented in immunohematology laboratories, and is proving to be a powerful tool, with potential advantages for identifying rare blood groups and finding better antigen matches for chroni¬cally transfused patients. Although superiority of genotyping over phenotyping is clear and reported for chronically transfused patients, there is no superiority for genotyping over phenotyping when performed to determine extended blood group typing for patients with no history of previous transfusion and negative antibody screen test, especially as genotyping is a more sophisticated and time consuming method In summary, molecular typing is a powerful tool for aiding pre-transfusion testing in a serology based laboratory as it can decrease the risk of transfusion reactions, especially delayed transfusion reactions to existing alloantibodies, and prevents alloimmunization. But it can, sometimes, give misleading results; therefore, we are cautious about interpreting the molecular type in isolation, and we will perform serological phenotyping. As it was found that the integration of serological and molecular tests in the immunohematology routine as well as the evaluation, resolution and classification of the discrepancies found will help in the correct interpretation of the results found and, consequently, in the increase of transfusion safety Our data suggest important recommendations that have to be implemented and become part of our routine practice in Assuit University Hospital Blood Bank Perform screening test on patient’s samples prior to cross matching to ensure safe transfusion practice. A practical, cost-effective, and reasonable approach for RBCs antigen typing should be performed before the first transfusion in thalassemic patients and issuing of antigen matched blood (at least for RH and Kell antigens) to reduce the risk of alloimmunization. Re-evaluation of new antibody formation for every case previously known to have alloantibodies against certain antigens should be performed before the next transfusion, as they are at risk of developing multiple alloantibodies after further transfusions. Perform genotyping for D antigen for all Rh negative donors and to be registered in a data base to detect week D antigens as anti-D alloantibodies were seen in our patients 1/12 (8.3%) although ABO-Rh D matched RBCs were used. Perform genotyping for patient with frequent previous transfusions for accurate assignment of his blood group typing to provide him with an appropriate blood unit to avoid hemolytic transfusion reaction.