Red blood cell alloimmunization in transfused patients on AZT

Significant numbers of patients receiving azidothymidine (AZT) develop anaemia requiring an adjustment of AZT dosage. Fear of red blood cell (RBC) alloimmunization may act as a deterrent to exposing a patient to long-term transfusion therapy which is the alternative to AZT dosage reduction or discontinuation. This retrospective study was done to assess the incidence of RBC alloimmunization in transfused patients on AZT. Records of 72 patients receiving long-term AZT were analysed to assess the incidence of alloimmunization. Other study parameters included duration of transfusion therapy, total number of pRBC units transfused/patient, alloantibody specificity, rates of autoantibody detection and their specificity. For comparison, a parallel analysis was carried out on 188 male patients transfused during the same period of time for chronic renal failure (CRF). Only one of 72 AZT patients (1.4%) developed an alloantibody compared with seven of the 118 CRF patients (5.9%) (P = NS). The incidence of autoantibodies and positive direct antiglobulin testing in the AZT and CRF populations was found to be similar (9.7% v. 7.6% respectively; P = NS). The two populations were similar with respect to mean number of pRBC units transfused (AZT: 10.5 v. CRF: 11.5 units; P = NS); however, there was a significant difference in the mean duration of transfusion therapy (AZT: 4.5 months v. CRF 19.4 months; P less than 0.001). We conclude there is an insignificant incidence of alloimmunization in the multiply-transfused AZT population. Furthermore, in this study the incidence of RBC autoantibodies in AZT patients appears to be low and no different from that of patients with chronic renal failure.