Should patients receiving RhIG who have a drop in hemoglobin that triggers a transfusion be given Rh positive or Rh negative red cells?
Since patients will develop positive antibody screens after infusions of IV RhIG, which type of red cells to transfuse is an issue: type-specific but crossmatch-incompatible D+ red cells or crossmatch-compatible D red cells. Standard practice is to issue crossmatch-compatible red cells that lack corresponding antigens to which patients have clinically significant antibodies in order to prevent red cell destruction. Therapy with IV RhIG for ITP breaks this principle in that the purpose is to sensitize and destroy autologous red cells and thereby block destruction of IgG-sensitized platelets.
The issue is complex. If the primary goal of treatment is to increase the platelet count as quickly as possible, selecting D-positive red cells would theoretically support the primary treatment objective. Conversely, selecting crossmatch-compatible D-negative red cells would be the optimal choice if unless anemia (and not platelet count) is the main concern.
The manufacturer of IV RhIG recommends that patients who require transfusion to treat anemia following IVH caused by IV RhIG therapy should receive D-negative red cells so as not to exacerbate ongoing IVH. They also caution against transfusing D-positive platelets in such circumstances.