Chris Kresser: Unfortunately we don’t know that much about sIgA, and what I have come to after pretty extensive research and talking with various lab directors of the tests that measure sIgA is that it should not be a target of treatment. Low or high sIgA itself with no other issues should not necessarily be cause for treatment, and the best way to look at it is as a kind of sidecar marker of dysfunction. And as you surmise in your question, it should basically be assumed to increase or decrease on its own with proper treatment of underlying conditions, and that is often what happens. However, it is often the last thing to improve, in my experience. You could eliminate the pathogens and get rid of everything, but the sIgA might still be abnormal, and it might not normalize until you do the rebuilding-the-healthy-gut protocol and restore healthy gut ecology.
I don’t think it adds a lot to the clinical picture and doesn’t require action outside of what you’re doing otherwise, but with one exception, which is, as you recall from the training, if it’s extremely low, then what you want to do is test all the immunoglobulins and make sure there’s not an immunoglobulin deficiency. If you see undetectable sIgA on a stool test, you probably should run that follow-up test just to be sure.