Intestinal permeability in allogeneic hematopoietic stem cell transplantation: A comprehensive review of measurement methods, clinical determinants and prognostic significance.

The role of intestinal permeability in patients undergoing allogeneic hematopoietic stem cell transplantation remains unclear. This narrative review aimed to critically analyze the available evidence regarding the dynamics, predictors, and prognostic significance of intestinal permeability in the allogeneic hematopoietic stem cell transplantation setting. PubMed was searched from inception to December 2025 to identify relevant studies. Inclusion criteria comprised articles that used any methodology to assess intestinal permeability in the allogeneic hematopoietic stem cell transplantation setting. Animal studies and non-English publications were excluded. Twenty-one studies were identified involving 1,130 patients that used 22 distinct methodologies, encompassing both probe-based and biomarker-based approaches. While most probe-based studies demonstrated significant temporal changes, biomarker-based methodologies yielded conflicting and non-significant findings. Consistent predictors of increased intestinal permeability across the transplantation course included the conditioning regimen, dietary interventions, intestinal microbiota, and immune response. Regarding the prognostic significance, studies reported heterogeneous and often conflicting results across most evaluated clinical outcomes. Although significant advances have been made in understanding the role of intestinal permeability in the allogeneic hematopoietic stem cell transplantation setting, substantial knowledge gaps remain. Future studies should use multiple complementary methodologies simultaneously to capture the different components of the intestinal barrier.