No - you don't 'cross the line' into Type 1 - if this is what has happened - you have actually had a different type of diabetes all along!
It is called LADA (Latent Autoimmune Diabetes of Adults) which can behave like Type 2 for sometimes years and also responds to normal Type 2 medical treatment - ie pills, diet etc - rather than solely to injected insulin like normal Type 1 - but as Type 1 is always caused by an autoimmune attack, it still isn't Type 1 even though in the finish - it also can only be treated with injected insulin, although it often still helps to also continue with the Metformin.
It's quite confusing, so don't worry if you can't get your head round it.
In any event - there is a blood test which can establish how much insulin your pancreas is actually producing called a C-peptide test although not every single Lab has the wherewithal to undertake it, so the blood sample has to be sent away to one that does, plus it takes some time, it's not a quick overnight job wherever it's done. Usually takes a couple of weeks to get the answers, instead of PDQ like most other tests.
In any event, the glipizide is again a tablet and this encourages your pancreas to produce more insulin and hence you are usually told to take it with a meal in the hope the extra insulin will deal with the increase in BG from the meal. Which is your pancreas is still capable of producing insulin may be fine - but if it isn't - it won't work! and in which case you most likely do have LADA.
