ABO-mismatched platelet transfusions: strategies to mitigate patient exposure to naturally occurring hemolytic antibodies.

Clinically significant hemolysis is a rare but potentially severe complication of administering an ABO-mismatched platelet transfusion. Platelet products from Group O donors, particularly single donor platelets (SDP) are most commonly implicated in these reactions. This is due to the presence of unusually high titers of anti-A which can be found in the plasma of some Group O donors and the large plasma volume of SDPs. These products can cause significant hemolysis when infused into a Group A or AB recipient. Random donor platelets from Group O donors have also been implicated. In practice, platelets are frequently transfused across ABO barriers though, ideally, in order to prevent or mitigate these reactions, platelet transfusions that are matched for ABO should be administered. However, limited availability of donor platelets as well as an abundance of Group O donors makes this a difficult standard to adhere to since often out-of group products are the only ones available. Methods to improve the safety of Group O products have focused on defining a safe level of isohemagglutinins so that the risk of hemolysis is alleviated when mismatched products are transfused. Determining the critical titer which defines a level above which a mismatched product should not be administered has been challenging. Non-standardized methods of isohemagglutinin titering and varying reports in the literature where products with a wide range of titers have been implicated in acute hemolytic transfusion reactions have made it difficult to determine a cut-off for labeling a product as high titer and thereby restricting its use to O recipients. Standards in the US place the responsibility for designing and implementing policies for the use of mismatched platelet products on each individual hospital transfusion service. Compliance requires only that there be an existing written policy which addresses the transfusion of products containing incompatible ABO antibodies but no specific procedures are required. In sharp contrast, European strategies have defined the low-end titer for which an out-of-group transfusion should not be given to an ABO-incompatible recipient. This testing is performed centrally at the Blood Centers who then make the determination on the status of a "dangerous donor". The progress in this European strategy may serve the US to stimulate a re-examination of its practices and policies for the advancement of platelet transfusion safety.