Reexposure to D-positive RHD genotyped units in D-positive chronically transfused patients with conventional RHD and unexpected anti-D. (A) All participants received 1 D-positive RHD genotyped unit for their first 2 study visits, and the remainder of units required for the RCE were Rh negative. For each subsequent visit, we added 1 D-positive RHD genotyped unit until all units for the RCE were D positive. Study subjects returned 5 to 12 days post-RCE for a complete blood cell count, hemoglobin quantification, antibody test, and comprehensive metabolic panel. (B) For each study subject (RH genotype indicated under their study unique patient identification [UPID]), the number of units with only conventional RHD alleles, heterozygous RHD/RHD∗DAU0, homozygous RHD∗DAU0, or Rh negative is indicated. At visit 5 for UPID 145, 1 of 4 D-positive genotyped units demonstrated incompatibility; 1 Rh-negative unit was substituted for transfusion. Genotyping of the incompatible D-positive unit revealed the donor was Lu14⁺, which UPID 35 was immunized against.