The prevalence, alloimmunization risk factors, antigenic exposure, and evaluation of antigen-matched red blood cells for thalassemia transfusions: a 10-year experience at a tertiary care hospital BACKGROUND: Hemoglobin E-β 0 thalassemia and homozygous β 0 -thalassemia are the most common chronic transfusion-dependent thalassemias in Thailand. Patients with these conditions can experience clinical complications such as RBC alloimmunization. In this study we aimed to determine the prevalence, alloimmunization risk factors, antigenic exposure, and evaluation of antigen-(C, c, E, e, Mi a ) matched RBC transfusion. STUDY DESIGN AND METHODS: Thalassemia patients were recruited from a tertiary care hospital for 10 years from 2008 to 2017. The medical records of transfusion history were reviewed for red cell phenotype both of patients and donors, number of units transfused, and type of alloantibodies. RESULTS: A total of 383 thalassemia patients were identified (178 males and 205 females). The frequency of RBC alloantibodies was 19.3%. Some patients tested positive for more than one antibody type. Autoantibodies were detected in nine individuals. Anti-E (49 [39.5%]), anti-Mi a (24 [19.4%]), and anti-c (19 [15.3%]) were the most common antibodies detected. A high rate of alloimmunization was found in splenectomized patients. Risk of alloimmunization increased when more total units of blood had been transfused. A trend toward low alloimmunization rates was noted in the antigen-matched RBC group, where 3.5% (5/143) of patients were alloimmunized. Anti-E and anti-Mi a , which may be naturally occurring, were identified in this group.CONCLUSION: Thai patients are more prone to develop antibodies against the Rh and Mi a than to the Kell blood group antigens.

We here report the first study of antigen and phenotype frequencies of Rh (C, c, E, e), M, Mia and Kidd antigens in north‐east Thai blood donors. Blood transfusion services aim to ensure availability of adequate and safe blood to minimize the development of transfusion reactions. For pre‐transfusion testing, the most important blood group systems are ABO and RhD. The transfusion of ABO‐compatible otherwise unknown phenotype blood may result in alloimmunization, especially in multi‐transfused patients. Extended red blood cell (RBC) phenotyping and selection of blood negative for specific antigens reduce post‐transfusion complications and allow for effective blood transfusion regimens to be achieved. A total of 13,567 regular repeated, voluntary Thai blood donors were included for red‐cell antigen typing of Rh (D, C, E, c, e). Samples from 12,768, 9,389 and 13,059 donors were typed for Kidd, M and Mia antigens, respectively. Amongst Rh antigens, e was the most common (96.80%) followed by C (95.50%), c (34.40%) and E (32.20%) with CCDee (60.00%) being the most common phenotype. For Kidd phenotypes, Jk(a+b+) was the most common (46.73%) and Jk(a−b−) was rare (0.07%). For the M and Mia antigen, M(+) was most frequently found (94.96%) and Mia(+) was found in 17.97% of individuals. Knowledge of red‐cell antigen phenotype frequencies in a population is helpful for creating a phenotype database of blood donors which can provide antigen‐negative compatible blood to patients with multiple alloantibodies. Moreover, provision of antigen‐matched blood can prevent alloimmunization in multi‐transfused patients.