Diagnostic difficulties in inflammatory bowel disease unclassified (IBD-U) - a narrative review

Abstract

BACKGROUND

Inflammatory bowel disease unclassified (IBD-U) is a diagnostic category used in patients with overlapping symptoms of Crohn's disease and ulcerative colitis in whom a definitive diagnosis cannot be made despite comprehensive clinical, laboratory, imaging, endoscopic, and histopathological evaluation. Although medical advances have improved diagnostic yield, IBD-U remains a significant clinical challenge due to its heterogeneous clinical presentation and the potential for subsequent diagnostic reclassification.

AIM OF THE STUDY

The aim of this review is to analyze and present the latest research on the problem of unclassified inflammatory bowel diseases, compare IBD-U with Crohn's disease and ulcerative colitis, and present the role of available diagnostic methods.

MATERIALS AND METHODS

A narrative review of the PubMed database was conducted. Original articles, systematic reviews, meta-analyses, and international guidelines published between 2011 and 2026 were analyzed. Studies addressing the epidemiology, clinical presentation, diagnostic methods, reclassification, and pediatric aspects of IBD were included.

DISCUSSION

The available evidence indicates that IBD-U is primarily a diagnosis of exclusion requiring comprehensive evaluation and long-term follow-up. Although ileocolonoscopy remains the cornerstone of diagnosis, magnetic resonance enterography, capsule endoscopy, and selected serological markers improve diagnostic accuracy in uncertain cases. Disease reclassification is common, particularly in pediatric patients, reflecting the dynamic nature of IBD-U.

CONCLUSION

Accurate diagnosis of IBD-U requires repeated multidisciplinary assessment rather than reliance on a single diagnostic test. Earlier identification of reliable biomarkers and refinement of diagnostic algorithms may improve disease classification and support more individualized patient management.