Secondary anti-D immunization by Del red blood cells

BACKGROUND: Recent molecular studies of the RHD gene have revealed that Del individuals retain a grossly intact RHD gene or have a portion of RHD in their genomes. No Del phenotype has yet been shown to induce a primary or secondary alloanti‐D immunization, however. CASE REPORT: A 67‐year‐old D– Japanese woman with a history of allosensitization from transfusion of D+ red blood cells (RBCs) was negative for anti‐D at admission. After she received RBCs from 19 apparently D– donors, she developed anti‐D with an 8‐fold titer. The titer of anti‐D increased further to 128‐fold after transfusions of cross‐match–compatible D− negative RBCs from 40 donors over the next 2 years. Two of 59 donors were found to be RHD gene–positive and antigen D– with a Del phenotype, that is, RHD(K409K). CONCLUSION: This is the first case in which RBCs having the Del phenotype induced a secondary alloanti‐D immunization. A D– donor with the RHD(K409K) allele was associated with the development of anti‐D. Adverse episodes or evidence of hemolysis was not observed after the transfusion of RHD(K409K) RBCs. Further clinical evidence is needed to reveal whether the Del phenotype has a clinically relevant potential for anti‐D immunization.