Abstract
Background and Objectives
Estimation of the frequency and causes of immunization to red blood cells in transfusion dependent thalassemia (TDT) patients can help us know the limitations of current practice and plan   specific measures to reduce it. This study aimed to evaluate the frequency and causes of immunization in TDT patients.
 
Materials and Methods
This case control study was conducted on 732 (TDT) patients between 20 November 2015 to November 2016 in  Dastgheib Hospital, Shiraz, Iran. Direct coombs test, antibody screening, and antibody identification were performed for every TDT patient. Then, the  frequency  and type of antibodies were surveyed. Clinical and laboratory data of immunized and non-immunized patients were compared.
 
Results
All of the case group had positive results in direct or indirect coombs tests. Indirect coombs test (ICT) was positive in 59 patients (63.4%) while direct coombs tests (DCT) was positive in 41 (44%) of immunized patients. In addition, 7 patients (7.52%) showed positive results for both DCT and IAT. The most frequent antibodies were against Kell (48.6%), D (22.7%) and E (18.2%). Our results reflected that lower age of starting transfusion and splenectomy had an impact on higher immunization rate.  
 
Conclusions 
Antbodies against Rh and Kell system were the most frequent antibodies. It seems that extended RBC matching at least for ABO/Rh/Kell antigens must be performed for thalassemia patients with its effect on RBC immunization rate to be then surveyed.