Fecal butyric acid as a predictive biomarker of endoscopic remission in inflammatory bowel disease: a multicenter prospective study.

Introduction: Effective prediction of endoscopic remission is a key to optimizing ulcerative colitis (UC) management. While fecal calprotectin (FC) is widely used, its limitations highlight the need for complementary biomarkers. This study evaluated fecal butyric acid (C4) as a novel, non-invasive predictor of endoscopic remission in UC. Aim: To assess the association between fecal C4 levels and endoscopic remission (Mayo score 0), and secondarily/also, the correlation between C4 and FC. Material and methods: A multicenter, prospective study enrolled 100 UC patients between April 2021 and April 2023, including 26 in remission and 74 with active disease. Inclusion criteria were confirmed UC diagnosis for ≥ 1 year and stable therapy without medication changes. Fecal C4 was measured using mass spectrometry. Analyses included descriptive statistics, group comparisons, receiver operating characteristic (ROC) curve analysis, and Spearman correlation. Results: Patients in remission had significantly higher fecal C4 levels (mean difference: 4.05 nM/mg; 95% CI: 2.44-5.71; p < 0.001) and lower Mayo scores. C4 showed excellent predictive performance (area under the curve (AUC) = 0.943; 95% CI: 0.897-0.980; p < 0.001), with 100% sensitivity and 86% specificity at a cutoff of 1.68 nM/mg. No significant correlation was found between C4 and FC. Conclusions: Fecal C4 is a promising biomarker for predicting endoscopic remission in UC, offering high sensitivity and specificity. Its use may enhance clinical decision-making and support individualized treatment approaches. Further validation in larger cohorts is warranted to confirm these findings and establish its clinical utility.