Peth testing is simply not well enough understood to stand on its own. It seems to have value in context with EVERYTHING else, just like they say.
Unfortunately there simply aren’t any appropriate studies yet. I’m working on that…
There are plenty of expert opinions available saying just this, and even opinions that false positives exist. There just aren’t studies showing the precise reason why…
Conversely, there aren’t studies showing peth testing is immune to error, merely empty statements that it’s only possible to get a positive test if you’ve been drinking.
I do believe the statement that peth is only formed if ethyl alcohol is present is likely accurate. However, where that alcohol comes from is highly debatable. To have SOME present is NOT a foolproof indicator of drinking, and I even believe the dried blood spot method of blood collection allows for post collection synthesis of alcohol itself.
Dried blood spot collection of blood is fraught with all sorts of problems, as evidenced by finger prick blood sugar devices.
Contact me offline if you want more info.