Fecal calprotectin as a biomarker for the diagnosis of gastrointestinal graft-versus-host disease following allogeneic hematopoietic stem cell transplantation.

Gastrointestinal graft-versus-host disease (GI-GVHD) is a major complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT), often requiring invasive endoscopy for diagnosis. Fecal calprotectin (FC) offers a non-invasive marker of intestinal inflammation, but its utility in GI-GVHD needs clarification. In this prospective observational study of 165 adult allo-HSCT recipients, FC was measured on days +7, +14, and +21 post-transplant, at GI-GVHD onset, and 7 days post-treatment, alongside clinical, endoscopic, and histological data. GI-GVHD developed in 52.7% of patients, with histological confirmation in 90.3% of cases. FC lacked predictive value on day +7 (AUC = 0.50) but showed moderate-to-high accuracy on days +14 (AUC = 0.69) and +21 (AUC = 0.77), with an optimal day +21 cutoff of 52.5 µg/g (sensitivity 75%, specificity 87%). At diagnosis, median FC was 120 µg/g, correlating with endoscopic severity (r = 0.31; p = 0.02) but not clinical or histological grades. FC declined significantly post-treatment (120 to 51.5 µg/g; p = 0.04), though concurrent infections elevated levels without compromising discriminative ability. FC serves as a dynamic biomarker for predicting, diagnosing, and monitoring GI-GVHD, but requires integrated clinical interpretation due to limited specificity amid other inflammations.