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Introduction The gut barrier is fundamental to human health and regulates the passage of molecules from the intestine into the blood stream. The permeability of the gut barrier is impaired in numerous health disorders including coeliac disease, inflammatory bowel disease (IBD), liver disease, and environmental enteropathy (EE, a multifaceted breakdown in gut function associated with undernutrition). Importantly, the role of the gut barrier in the above conditions is still not fully understood. Furthermore, current approaches to assess intestinal barrier function are expensive, invasive, unreliable and/or difficult to perform in certain populations. Thus, there is an urgent need for novel tests that can be deployed at scale to improve assessment and understanding of gut barrier function in EE and other diseases.Methods To begin to address these issues, we used transcutaneous fluorescence spectroscopy (TFS) to investigate intestinal barrier function in EE. TFS involves participants receiving an oral dose of a fluorescent contrast agent (fluorescein) and a wearable probe being placed on the fingertip to non-invasively assess uptake of fluorescein from the gut into the blood stream (via ‘through-the-skin’ fluorescence measurements). Volunteers were recruited in a Zambian community where EE is prevalent (n=34) and in the UK (n=17) to undergo TFS measurements in a cross-sectional study. TFS data were first compared between groups. Second, in a subset of 14 Zambian participants, TFS data were correlated with the lactulose:rhamnose (LR) test.Results TFS demonstrated significant differences in intestinal barrier function between UK and Zambian volunteers. Zambian participants exhibited higher peak fluorescence intensity (p=0.003) and area under fluorescence curves (p=0.02) than UK participants ( figure 1A), suggesting increased fluorescein permeation. Time to reach peak intensity was consistent between groups, indicating no differences in factors affecting uptake rate (e.g. gastric emptying, gut motility). Finally, fluorescence kinetics and regression analysis revealed strong correlations between TFS data and urinary recoveries of lactulose and rhamnose (Spearman’s r≥0.78, p<0.002; figure 1B).Conclusions TFS revealed differences in intestinal barrier function between EE and healthy cohorts using a rapid, sample-free methodology. Combined with exploratory results demonstrating correlation to the LR test, this implies potential to facilitate more advanced study of the role of the gut barrier in health and disease.Abstract P380 Figure 1(A) Mean (± standard deviation) TFS time courses recorded in Zambian and UK participants. Inset shows box plot of total area under curve (AUC). (B) Scatter plots showing correlation between actual percentage recoveries of lactulose and rhamnose and values predicted using TFS regression analysis.