Hemophagocytic Lymphohistiocytosis After Allogeneic Stem Cell Transplantation

Hemophagocytic lymphohistiocytosis (HLH) is a severe inflammatory complication that can occur after allogeneic hematopoietic stem cell transplantation. Its signs can overlap with those of infection and other transplant complications, making early recognition difficult. This study will examine whether changes in routine blood tests and clinical information can help identify patients who may develop HLH during the following seven days. The study will combine a review of existing medical records with prospective follow-up at participating hospitals in China. Approximately 20,000 adults undergoing their first allogeneic transplantation will be included, with approximately 400 post-transplant HLH cases expected. Historical records will be used to develop the prediction model. Data from independent centers and prospectively enrolled patients will be used to validate the model. Participants will be followed for one year after transplantation. Those who develop HLH during that year will also be followed for 90 days after HLH onset. The study will describe HLH occurrence, associated factors, treatments, and survival. All tests and treatments will remain part of routine care. No additional research samples or laboratory tests will be required, and model predictions will not be used to guide treatment.

Inclusion Criteria: * Age 18 years or older at first allogeneic hematopoietic stem cell transplantation. First allogeneic hematopoietic stem cell transplantation performed at a participating center within the study period. Verifiable transplantation date and basic clinical information. Written informed consent from the participant or legally authorized representative for prospective participation. Retrospective records are used under the applicable ethics-approved consent or waiver procedures. Exclusion Criteria: * Autologous transplantation or transplantation other than hematopoietic stem cell transplantation. HLH diagnosed before transplantation, or transplantation performed primarily for HLH. Previous allogeneic hematopoietic stem cell transplantation. Patient identity, transplantation date, or key outcome information cannot be verified. Explicit refusal to participate or to permit the use of clinical information for this study.