Development and validation of the Red Flags Index for Crohn's disease in high-risk populations in Korea

The increasing prevalence of Crohn's disease (CD) in South Korea has led to complications and reduced quality of life, emphasizing the need for early, non-invasive diagnosis. The International Organization for Inflammatory Bowel Disease (IO-IBD) developed the Red Flag Index (RFI) for early CD detection; however, it remains to be validated in the Korean population. This study aimed to develop and validate a Korea-specific RFI for early CD diagnosis using clinical and biomarker data.

Data from 121 patients with CD at Seoul National University Hospital were compared with those from two control groups: Group A (101 non-CD individuals) and Group B (198 high-risk individuals). The participants answered 15 IO-IBD-derived questions. Chi-square tests and logistic regression were used to identify key RFI predictors. Receiver operating characteristic (ROC) analysis was used to evaluate diagnostic performance, with subgroup analyses adjusted for RFI scores. The effect of fecal calprotectin on accuracy was also assessed.

RFI identified key CD predictors: perianal lesions, weight loss, chronic anemia, chronic/nocturnal diarrhea, perianal pain, male sex, and fecal calprotectin >100 µg/g. The RFI's area under the curve (AUC) was 0.77 (Control A) and 0.88 (Control B), improving to 0.878 and 0.92, respectively, with fecal calprotectin. Subgroup analyses confirmed RFI's enhanced diagnostic accuracy, particularly in high-risk groups, except for the ankylosing spondylitis subgroup, which had lower AUCs.

RFI demonstrated strong diagnostic performance, particularly when combined with fecal calprotectin, reinforcing its applicability in stratifying high-risk populations for early and accurate CD detection.