Evaluation of Tryptophan and Its Metabolites in Predicting Disease Activation in Inflammatory Bowel Disease

Background and Aim: Inflammatory bowel disease (IBD), which comprises ulcerative colitis (UC) and Crohn's disease (CD), is characterized by chronic inflammation and fluctuating disease activity. This study aimed to evaluate serum tryptophan (TRP) and its metabolites as potential biomarkers for predicting disease activation in comparison to fecal calprotectin (FC). Methods: This prospective study included 115 patients (77 with UC and 38 with CD). Disease activity was assessed based on clinical and endoscopic findings. Serum TRP levels and their metabolites were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS), whereas FC levels were analyzed using an enzyme-linked immunosorbent assay (ELISA). Results: Serum TRP levels ≤ 11,328.41 ng/mL predicted disease activation with 72.1% sensitivity and 62.7% specificity, whereas FC levels ≥ 89.60 µg/g showed 84.2% sensitivity and 67.6% specificity. The TRP-to-C-reactive protein (CRP) ratio (TRP/CRP) demonstrated superior diagnostic accuracy, with an area under the curve (AUC) of 0.847. Conclusions: The TRP/CRP ratio is a novel and comprehensive approach for predicting disease activation in IBD patients. Although FC remains the gold standard, TRP and its metabolites provide valuable complementary insights. Further research is required to validate these findings in larger cohorts.