Cherry, well, yes, prolonged gluten damage can lead to irreversible damage in various organs, including diabetes - when you have damaged something beyond repair then the blood results would definitely confirm a disease.
Unfortunately, most doctors will want to see a disease rather than consider prevention before it turns into a disease.
Biopsy can also be inconclusive - the gut is 6m long and they only take a microscopic sample. You would have to be quite ill for it to guarantee the result. If the borderline sensitivity turns into autoimmune condition (like thyroid etc), then you would not be able to remove antibodies and you would have less chance of reversal boderline damage.
Another book which explains how gluten can affects various parts of the body is "Dangerous Grains" by Braly & Hogan.
It's all very complex, but what got me into gear was when a neurologist confirmed that gluten damage (to the brain in our case) can be irreversible - well, I didn't want to wait to see all of it, because my son already had some symptoms. Thankfully, many have improved.
When I found quite recently that his pancreas is low functioning (that could easily lead to diabetes!!) I was glad that we had intercepted further damage by going on the diet. Yes, it's scary, not just googling, but discovering how symptoms link and how serious this can get. Only understanding it really helped me, because otherwise you would just be chasing symptoms, because other organs can also be affected. You often hear that some conditions like diabetes don't come with a bang - they build up over a period of time - and that is almost certainly a result of unresolved gluten damage.
Also, have a look at the link below, quite good too.
link