Table 1.

Methods to assess intestinal permeability

Methods	Assay	Advantage and disadvantage	References
Morphology analysis	H&E staining of intestinal sections	Histology is easy to perform and to interpret No functional analysis	(Szabo et al., 1985)
	Assessing intestinal tight junctions (electron microscopy, gene and protein expression)	No functional analysis	Hartmann et al., 2012; Chen et al., 2014a
Functional analysis
Methods to assess flow from lumen to blood	Enteral administration of non-digestible markers such as sugars, radioisotopes (e.g. 51Cr-EDTA) and polyethylene glycols (PEG)	Performed under in vivo conditions, but affected by factors such as gastrointestinal motility, mucosal blood flow and the distribution of the markers in the body Inert markers are being used	Sun et al., 1998; Bjarnason et al., 1984a; Bjarnason et al., 1984b; Peeters et al., 1994
	Creating isolated intestinal loops and injection of labeled bacterial products, markers or live bacteria	Serves with modifications a wide variety of purposes and are independent from intestinal motility Able to determine the site of increased leakiness Surgery required	Chen et al., 2014a Hartmann et al., 2012; Hartmann et al., 2013
Methods to assess flow from blood to lumen	Fecal albumin measurement	Non-invasive, does not require any manipulation of the animal.	Hartmann et al., 2013
	In vivo perfusion system	Requires normal blood albumin levels Can be used to test the effects of drugs on intestinal permeability Surgery required	Clayburgh et al., 2006; Marchiando et al., 2010b
Microbiology tests	Measurement of translocated microbial PAMPs	Direct assessment of gut-derived and translocated PAMPs in extraintestinal space Levels are dependent on the immune system	Hartmann et al., 2012; Chen et al., 2014a; Chen et al., 2014b; Cuenca et al., 2014
	Culturing translocated live bacteria	Direct assessment of gut-derived and translocated bacteria Numbers are dependent on the immune system Not able to detect non-culturable translocated bacteria	Fouts et al., 2012