I wouldn't recommend treating something that you haven't confidently identified yet. hba1c gives a picture of blood glucose levels over the past 3 months or so, but one reading of an acute blood sugar level isn't something I would base conclusions on, despite the other symptoms.
If he is evaluated for diabetes by a physician, keep in mind if your concern is the medications, he doesn't have to take them. I think a diagnosis and consultation could go a long way. I don't know of any inordinate harm associated with a blood draw to test for markers like hba1c levels that would give a broader picture.
I do have my biases. But I generally don't see inordinate complications with getting a good dataset. What happens after the data is laid out tends to be when opinions diverge.