RESUMEN
Transport of molecules across the intestinal epithelium takes place through 2 major routes, ie, trans-cellular and paracellular. Assessment of intestinal permeability is performed to assess the overall function of transport through the intestinal epithelial paracellular route. Urinary excretion of disaccharides and monosaccharides and ratio of their excretion is a basis for measurement of intestinal permeability. Lactulose and mannitol ratio is the most commonly used test for assessment of small intestinal permeability and the most reliable method for measurement of concentration of lactulose and mannitol in the urine is high performance liquid chromatography. After the measurement of concentration of probes in the urine; the results are expressed as the ratio of percentage excretion of the ingested dose of lactulose and mannitol in the urine. Testing of intestinal permeability is not required for routine patient care, however it is an important tool to understand the function of the paracellular transport in the research setting. Increase in intestinal permeability has been implicated in the pathogenesis of many autoimmune diseases including celiac disease, Crohn's disease, type I diabetes and food allergy.