Serum Zonulin and Chitinase (CHI3L1) as Biomarkers of Intestinal Permeability and Disease Activity in Pediatric Celiac Disease.

Objectives: To evaluate serum zonulin and CHI3L1 as indicators of intestinal permeability and disease activity in pediatric celiac disease and to explore their associations with histopathological findings and nutritional status. Methods: This prospective cross-sectional study included 131 pediatric patients with CD (aged 2-18 years) and 42 healthy controls. Patients were classified as newly diagnosed, gluten-free diet (GFD)-adherent, or GFD-nonadherent. Body mass index was calculated, and serum levels of micronutrients, zonulin, and CHI3L1 were measured using a sandwich enzyme-linked immunosorbent assay. Associations with histopathological findings, serological markers, and nutritional parameters were analyzed. Results: Age and sex distributions were similar across groups (mean age: 10.9 ± 4.27 years). Serum zonulin and CHI3L1 levels were moderately positively correlated (r = 0.525, p < 0.001). Both biomarkers showed significant positive correlations with Marsh scores and tissue transglutaminase IgA levels. Zonulin was inversely correlated with hemoglobin, serum iron, and ferritin, whereas CHI3L1 showed negative correlations with hemoglobin and folate. Parathyroid hormone levels were positively correlated with both biomarkers. Receiver operating characteristic analysis demonstrated acceptable discriminatory performance for distinguishing CD from controls (AUC: 0.713 for zonulin and 0.709 for CHI3L1). Conclusions: Serum zonulin and CHI3L1 levels are associated with disease activity and mucosal injury in pediatric CD but do not directly reflect micronutrient status. These biomarkers may complement conventional monitoring parameters by providing additional information on intestinal permeability and inflammatory activity during follow-up.