Reactivity of FDA-approved anti-D reagents with partial D red blood cells

Individuals whose RBCs are characterized as having a partial D phenotype may make anti-D if exposed to normal D+ RBCs; thus it is desirable that they be typed as D- should they require blood transfusion or Rh immune globulin (RhIG) prophylaxis. Further, use of different anti-D reagents by blood centers and transfusion services can account for FDA-reportable errors. For this study, anti- D reagents for use in tube tests were obtained from three U.S. manufacturers. They included three examples of IgM monoclonal anti-D blended with monoclonal IgG anti-D, one IgM monoclonal anti-D blended with polyclonal IgG anti-D, and two reagents formulated with human anti-D in a high-protein diluent. One anti- D formulated for use by gel column technology was also tested. Direct agglutination tests by tube or gel were strongly positive (scores 9-12), with partial D RBCs of types DII, DIIIa, DIIIb, and DIVa. No reagent anti-D caused direct agglutination of DVI type 1, DVI type 2, or DFR phenotype RBCs. One tube anti-D reagent formulated with an IgM monoclonal anti-D plus a polyclonal IgG anti-D failed to cause direct agglutination of DVa, DBT, and R(0)(Har) RBCs, while DVa RBCs reacted weakly with two high-protein reagents formulated with human IgG anti-D. In contrast, the anti-D used by gel column technology was strongly reactive (score 11) with DVa, DBT, and R(0)(Har) RBCs. The single monoclonal IgM-polyclonal IgG blended anti-D and the two high-protein reagents were also the only reagents that failed to react with R(0)(Har) RBCs by the IAT. Elimination of the test for weak D on all patient samples, using currently available FDA-licensed reagents, will ensure that partial D category VI (DVI) patients will type as D- for the purpose of RhIG prophylaxis and blood transfusion. However, RBCs of other partial D phenotypes will be classified as D+ in direct agglutination tests with some, if not all, currently available reagents. Testing donors for weak expression of D continues to be required, albeit that Rh alloimmunization by RBCs with a weak or partial D phenotype is uncommon. Further, because of differences in performance characteristics among FDA-approved reagents, conflicts between donor center D typing and transfusion service confirmatory test results are inevitable.