Secondary alloanti-D immunization post transfusion of "Asia type" DEL red blood cells

BACKGROUND: "Asia type" DEL red blood cells (RBCs) express a very weak D antigen and cannot be detected by routine RhD typing. Thus, it is routinely typed as D-negative (D-) blood group and transfused to D- recipients. Here we described a case of secondary alloanti-D immunization that was associated with transfusion of DEL RBCs to D- recipients and was initially considered as primary alloanti-D immunization. CASE PRESENTATION: A 44-year-old D- woman (G2P2) with adenomyosis and anemia underwent transabdominal hysterectomy. She received four units of D- RBCs before operation. Before transfusion, the alloantibody screening test was negative. Four days after the first transfusion, she needed another RBC transfusion. Unexpectedly, the routine pre-transfusion alloantibody screening test became positive and anti-D (titer, 128-fold) was identified, indicating an alloanti-D immunization. The anti-D developed four days after the first transfusion was unexplained, so alloantibody identification was performed on the sample collected before the first transfusion, and weak anti-D combined with anti-E, which was not detectable during the previous routine pre-transfusion alloantibody screening test with non-enzyme-treated screening cells, was identified using bromelain-treated panel cells. The remaining blood samples of first transfusion in bag tails from two donors were collected for RHD genotyping analysis. One donor was later identified as "Asia type" DEL having RHD* 1227 A/01 N.01 genotype. CONCLUSION: Caution should be applied when we conclude that transfusion of "Asia type" DEL RBCs to true D- recipients could induce primary alloanti-D immunization, especially if the short time interval between transfusion and detection of anti-D is observed.