Prevalence of Alloimmunization Among Patients With Transfusion-Dependent Thalassemia and Sickle Cell Disease in Salmaniya Medical Complex, Bahrain.

Background Red blood cell (RBC) alloimmunization is a significant complication among patients with transfusion-dependent thalassemia and sickle cell disease (SCD), potentially leading to difficulties in crossmatching, delayed hemolytic transfusion reactions, and hyperhemolysis. In Bahrain, the prevalence of RBC alloimmunization among patients with hemoglobinopathies had not been previously reported. Objective  To determine the prevalence of RBC alloimmunization among patients with transfusion-dependent thalassemia and SCD in Bahrain and to compare findings with published regional and international data. Methods  A retrospective, cross-sectional study was conducted at Salmaniya Medical Complex (SMC), Bahrain. A total of 311 transfusion-dependent patients, 203 with SCD and 108 with thalassemia, registered between 2016 and 2025 were included. Clinical and laboratory data were extracted from electronic medical records. Patients with a positive indirect antiglobulin test (IAT) showing a consistent reaction strength of 2+ or greater were considered alloimmunized. Descriptive statistics were used to analyze demographic variables and determine the prevalence of alloimmunization. A chi-square test was used to compare alloimmunization rates between the SCD and thalassemia groups. The rates observed in this study were also compared with those reported in other countries using chi-square analysis. A p-value < 0.05 was considered statistically significant.  Results The overall prevalence of RBC alloimmunization was 14.8%. Alloimmunization was significantly more prevalent among patients with SCD, with 41 out of 203 (20.2%) testing positive, compared to only 5 out of 108 (4.6%) patients with thalassemia (p < 0.001). Among the 46 alloimmunized patients, 58.7% were male, and 41.3% were female, reflecting the sex distribution of the study population. Blood group O was the most common (54.3%), and 95.5% of patients were Rh-positive.  Conclusion The alloimmunization rates observed in this study are consistent with the rates reported in other Middle Eastern countries. Despite extended phenotypic crossmatching, patients with SCD had a significantly higher alloimmunization rate than patients with thalassemia, likely due to disease-related immune activation and differences in transfusion protocols. Adoption of molecular RBC genotyping and comprehensive antibody identification for all alloimmunized patients is recommended to improve transfusion safety in this population.