Materials and methods

Study design and setting

This retrospective, cross-sectional study was conducted at Salmaniya Medical Complex (SMC), the largest tertiary care hospital in Bahrain, after obtaining approval from the Research Committee for Government Hospitals (no. 76-310725).

Inclusion and exclusion criteria

This study included patients of all ages with transfusion-dependent thalassemia or SCD who were registered in the hospital blood bank between 2016 and 2025. Patients with transfusion-dependent thalassemia received simple transfusions every 2-4 weeks, whereas patients with transfusion-dependent SCD received exchange transfusions every 3-8 weeks. Patients were eligible for inclusion if they had undergone at least one indirect antiglobulin test (IAT) during the study period. Patients were excluded if their records were incomplete, specifically for cases in which no IAT was performed between 2016 and 2025. A total of 311 patients, 203 with SCD and 108 with thalassemia, met the eligibility criteria and were included in this study.

Data collection

Clinical and laboratory data were extracted from I-SEHA, the hospital’s electronic medical records system. The collected data included demographic characteristics (age, gender, ABO blood group, and Rh factor) and alloimmunization status. Patients who had a positive IAT with a consistent reaction strength of 2+ or greater were considered alloimmunized. Patients with consistently negative or weakly positive IAT reactions were not classified as alloimmunized.

Laboratory methods

Whole blood samples were collected in ethylenediaminetetraacetic acid (EDTA) tubes, transported to the blood bank under standard conditions, and processed within 24 hours of collection.

Pre-transfusion testing throughout the study period followed SMC blood bank policy and included ABO and RhD typing, antibody screening, and compatibility testing. Antibody screening was performed for all patients using an IAT-based gel column agglutination method with commercially prepared screening cells (0.8% Selectogen; Ortho-Clinical Diagnostics, Inc., NJ, USA). A direct antiglobulin test (DAT) was also performed as part of the routine pre-transfusion workup.

Antibody identification to determine specific alloantibody types and frequencies was performed only on a limited subset of patients with reactive screens using standard reagent red cell panels (0.8% Resolve Panel A; Ortho-Clinical Diagnostics, Inc., NJ, USA). The decision to perform antibody identification was either based on the clinician’s request or at the discretion of the transfusion medicine and blood banking physician.

Statistical analysis

Descriptive statistical analysis was performed using IBM SPSS version 29 (released 2022; IBM Corp., Armonk, NY). The software was used to determine the frequencies and percentages of demographic variables and the prevalence of alloimmunization within the studied population. Chi-square tests were then used to compare alloimmunization rates between the SCD and thalassemia groups, and to compare the rates observed in this study with those reported in other countries. A p-value of less than 0.05 was considered statistically significant for all comparisons.