Clinical Performance of Fecal Calprotectin Reagents Based on the Colloidal Gold Agglutination Method for Evaluating the Differential Diagnosis between Inflammatory Bowel Disease and Irritable Bowel Syndrome in Adults and Children with Gastrointestinal Symptoms (SCALE 1).

Introduction: Fecal calprotectin (FC) reliably reflects both clinical and endoscopic disease activity in inflammatory bowel disease (IBD) and helps differentiate IBD from irritable bowel syndrome (IBS). The aim of this study was to determine the diagnostic utility of FC using the colloidal gold agglutination (CGA) method in distinguishing active-phase IBD from IBS in both children and adults. Methods: This prospective, multicenter, observational study was conducted across eight participating institutions. The primary goal was to validate the discriminatory ability and reference values of FC using the CGA method between patients with IBD in the active phase and those with IBS. Results: A total of 285 patients were analyzed, including 205 with ulcerative colitis (UC), 24 with Crohn's disease, and 56 with IBS. In the receiver operating characteristic (ROC) curve analysis, FC demonstrated very high specificity (98%) for differentiating patients with active-phase IBD from those with IBS when a cutoff value of 500 µg/g was applied. With respect to endoscopic evaluation, the correlation between FC and cumulative endoscopic scores, which were calculated by summing segmental scores across the colon, was stronger in pediatric patients with UC (MES, Conclusion: FC measured using the CGA method proved to be a reliable and clinically meaningful biomarker for differentiating active IBD from IBS in adults and active UC from IBS in children. Comprehensive evaluation with cumulative endoscopic scores can be useful for understanding disease activity in pediatric patients with UC.