A survey of transfusion support strategies for passenger lymphocyte syndrome in minor <scp>ABO</scp> ‐mismatched allogeneic hematopoietic stem cell transplantation

BACKGROUND: Passenger lymphocyte syndrome (PLS) is a hematologic complication of ABO blood-type minor incompatibility that can occur following both solid-organ and hematopoietic stem cell transplant (HSCT). HSCT patients usually require red blood cell (RBC) transfusions until they achieve full erythroid engraftment. It is unclear whether the blood bank should honor the recipient's blood type or the donor's blood type at the time of issuing RBC products for minor ABO-incompatible HSCT patients prior to full engraftment. To avoid this confusion, blood group O RBCs are often transfused. However, the role of this approach in the prevention of PLS in minor ABO-mismatched HSCT recipients prior to full engraftment is not well understood. STUDY DESIGN AND METHODS: We conducted a survey of academic hospital blood banks across the United States in October-December 2025 to assess their practices for providing RBC transfusion support to minor-incompatible HSCT patients. RESULTS: Sixteen out of 24 hospital blood banks, including adult and pediatric centers, responded to the survey. The majority reported providing crossmatch-compatible type O RBC to recipients with blood types A, B, or AB, regardless of engraftment outcome. Five do not routinely transfuse O RBC. Two hospitals had one patient each with PLS resulting in severe intravascular hemolysis, and 11 reported mild PLS despite providing crossmatch-compatible type O RBC products to recipients. CONCLUSION: Regardless of the blood type of the transfused RBC, mild PLS can occur in minor ABO-incompatible HSCT patients prior to full engraftment.