RESUMO
Repeated transfusions for the treatment of thalassaemia major cause an insult to the patient's immune system and provoke post-transfusion purpura and haemolytic reactions that can be severe and life threatening. This study aims to investigate the presence of erythrocyte autoantibodies and CD59 expression on the surface of red blood cells (RBCs) in patients with beta-thalassaemia major, and any relationship to frequency of blood transfusion. The study looks at a total of 49 patients (both children and adults) with beta-thalassaemia major, divided into four groups according to the number of blood transfusions received and the presence or absence of the spleen. Glycosylated haemoglobin, Coombs' test (direct and indirect) and CD59 level on the RBC surface (by flow cytometry) are estimated in all patients studied. Glycosylated haemoglobin level was significantly lower in those who had received less than 10 units of blood (group III) than in those who had received more than 25 units of blood and had undergone splenectomy (group Ib), and was significantly lower in those who had received 10-25 units of blood (group II) than in those that comprised group Ib (F=3.598, P=0.0205). Considering CD59 expression, there was a marked difference between the groups. Expression was highest in group III and diminished progressively through groups II, Ia (polytransfused, non-splenectomised) and Ib (F=19.83, P=0.0000). No relationship was observed between CD59 expression and either blood group or gender. A significant negative correlation between CD59 expression and reticulocyte percentage (r=-0.538, P=0.000) and normoblast count (r=-0.5455, P=0.000) was found. A negative correlation between lymphocytosis and CD59 expression was also noted in groups III (r=-0.745, P=0.013), Ia (r=-0.5849, P=0.022) and Ib (r=-0.6711, P=0.009). Direct Coombs' test was positive in only one patient in group Ib, who also showed the lowest haemoglobin level. Thalassaemia patients exposed to multiple antigens through repeated blood transfusions showed lower CD59 expression than did those who had received fewer transfused units, which is a good method of detecting potential autoantibodies. Furthermore, a negative Coombs' test does not exclude autoimmunisation in such patients.
