Supplementary Material for: Two cases of anti-D alloimmunization in D-negative Thai patients as a result of the Asian type DEL on transfused red cells.

Introduction: DEL is known to be one of the weakest D variants, which can be detected by the adsorption-elution technique or by molecular study. Currently, in Thailand, we do not routinely test for DEL variant serologically or genetically among serologic Rh D negative blood donors. Case Presentation: We reported two cases of alloimmunization after transfused with Rh DEL, RHD*DEL1 allele, in the Thai population. The first case was a 73-year-old male with anemia who presented with post-cardiac arrest and septic shock. The patient was group B, RhD negative, and was transfused with RhD negative red blood cells (RBCs). Antibody screening and identification found that the patient developed anti-D and anti-Mia during the admission course. The second case was a 38-year-old woman with pseudomyxoma peritonei who developed anti-D after receiving four units of RhD negative RBCs during cytoreductive surgery with hyperthermic intraperitoneal chemotherapy. Both patients did not receive anti-D immunoglobulin and had no previous history of anti-D detection. We retrospectively investigated and found two units of RHD*DEL1 among the RBCs transfused to these patients. Discussion: Previous reports of several cases of anti-D alloimmunization in RhD-negative recipients transfused by RHD*DEL1, an Asian-type DEL, are limited only in East Asiaand one case in Austria. We first identified two patients with anti-D alloimmunization after receiving the RHD*DEL1 RBCs in the Thai population. This raises concern about Rh DEL screening among D-negative Thai blood donors and whether to remove DEL units from the D-negative inventory to improve patient safety.