Transfusion practice in allogeneic hematopoietic stem cell transplantation: a narrative review of clinical guidelines and evidence gaps

Transfusion support is a cornerstone of care for patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT), yet many aspects of transfusion practice remain controversial due to limited high-quality evidence. Conditioning regimens induce profound cytopenias, making red blood cell (RBC) and platelet (PLT) transfusions essential. Transfusion requirements vary according to transplant modality, with cord blood and haploidentical transplants associated with higher needs. ABO incompatibility, present in up to 50% of transplantation procedures, is not a contraindication but may lead to immunohematological complications such as passenger lymphocyte syndrome and pure red cell aplasia. The objective of this review is to summarise the current guidelines on transfusion management for HSCT patients focusing on evidence GAPs and unresolved issues.