The topic of "Leaky Gut" is a contentious one.
On one side of the spectrum, most alternative providers think nearly everyone is affected by Leaky Gut, because of the long list of alleged symptoms -- which, by the way, overlap with many other conditions, too.
At the other end of the spectrum, there are doctors that state the condition doesn't exist. They do acknowledge that "Intestinal Permeability" exists, but they clarify that it's different than what Leaky Gut claims to be. Furthermore, they state that Intestinal Permeability is the result of various ailments and not a cause.
Standard medicine is slow to adopt new ideas and testing methods, while alternative providers stretch the bounds of what can be proven. So, like many things, the truth is probably somewhere in the middle.
I know Cyrex Labs offers "Array 2 - Intestinal Antigenic Permeability Screen" that measures markers such as Actomyosin, Occludin/Zonulin, and Lipopolysaccharides.
https://www.cyrexlabs.com/cyrextestsarrays/tabid/136/default.aspxPerhaps that's something to consider, if you have a provider that can (1) order the test, (2) properly interpret the results, and (3) knows what to do with the information.
You could try something simpler and cheaper (possibly covered by insurance), such as the test where you drink a solution of Lactulose and Mannitol and then collect your urine over the next six hours. Then, the urine is analyzed to check for the levels of each sugar. I've heard that if the test is positive (for intestinal permeability), then it's probably valid, as the degree of dysfunction would likely be significant. However, if the test were negative, that wouldn't necessarily mean there was no gut dysfunction.