Hemoglobin E‐β⁰ thalassemia and homozygous β⁰‐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.

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.

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.

Thai patients are more prone to develop antibodies against the Rh and Mi^a than to the Kell blood group antigens. Provision of at least antigen‐matched (C, c, E, e, Mi^a) RBCs appears to improve the efficacy of transfusion in thalassemia patients.