Tools and advanced imaging technologies for assessing intestinal epithelial barrier integrity: a systematic review

The intestinal epithelium is a key component of the intestinal barrier, which is the largest and most complex barrier of the human body, regulating nutrient absorption while restricting the entry of harmful antigens. Breakdown of this barrier facilitates microbial and dietary antigenic translocation, triggering local immune system activation and inflammation. Although barrier alteration alone may not be sufficient to initiate disease, accumulating evidence highlights its critical role in the pathogenesis and progression of a wide range of gastrointestinal and systemic disorders. Early identification of intestinal epithelium and barrier alterations could enable timely therapeutic approaches. This systematic review provides an overview of current in vivo (both noninvasive and invasive) and ex vivo/in vitro approaches used to assess intestinal epithelial barrier alterations. Noninvasive in vivo approaches rely mainly on urinary detection of orally ingested probes, but their clinical utility is limited by lack of standardization and specificity. Circulating and fecal constitutive markers derived from the intestinal barrier, which reflect epithelial alterations, together with indicators of microbial translocation, provide complementary insights but remain insufficiently validated. Advanced invasive endoscopic modalities such as confocal laser endomicroscopy enable near-histological, real-time visualization but are costly and largely used as research tools in specialist centers. In vitro, transepithelial electrical resistance assessment remains the reference standard, though novel technologies (including impedance spectroscopy and organic electrochemical transistors) offer enhanced sensitivity and resolution. Despite progress, major gaps remain, including the absence of a standardized definition of epithelial barrier breakdown, the lack of a practical diagnostic tool, methodological heterogeneity, unvalidated thresholds, and limited prospective validation.