The thing is it wouldn't have been expensive to test. In the article they describe the testing they did after they treated her for auto-brewery syndrome. The

The thing is it wouldn't have been expensive to test. In the article they describe the testing they did after they treated her for auto-brewery syndrome. The gave her an oral administration of glucose and then observed her alcohol levels. It would lead me to believe a pretty easy means to diagnose auto-brewery would be to check BAC, give them glucose and then retest BAC. If it goes down they at the very least aren't currently suffering from auto-brewery. If it goes up, that would be a pretty strong indicator they are suffering from it. Have an orderly or nurse observe to verify no alcohol was consumed if you want.