Hi Hendie,
I'm in a similar HbA1c range as you this is what happened.
Last year I started to need to pee a lot, but more so in the night I thought my Interstitial Cystitis had returned. I always had the need to drink water more than people I know, and when I got hungry I just HAD to eat or I would become very moody and listless...I did have the 'foggy head' but ignored it because I thought it was from getting up at night to pee so I was tired.
They did a urine test in Nov and said my glucose was slightly raised and asked if there Diabetes in the family (both parents are T2) They told me I would needed to be checked out further. My GP wrote to me to come in and the nurse did a fasting glucose test and an HbA1c in Dec, my GP also took blood for everything because I told him I was just generally feeling under the weather.
And they did fasting glucose and Hba1c in March. Because I was over the 6 mark both times this was their basis for a diagnosis of Diabetes.
You can see my HbA1c results and dates below.
A c-peptide test can be done regarding insulin (but it can come up normal) BUT it just tells you that you're producing insulin - it doesn't confirm how much of it is being used up. I had this done and it was normal.
I don't think this is a standard test they offer to all people that they're testing for Diabtetics, they did it to me as I don't fit the 'standard criteria for T2' i.e normal BMI, weight and age is 34. If someone has extra weight it's assumed that there's fat around the internal organs and this contributes to insulin resistence - this is what the specialist has told me.
So it still doesn't tell me why my insulin is not helping my glucose get into my cells, but at this stage I'm not overproducing insulin so I suppose because my overall control is regarding as good control...I don't know, they don't really know. It's a waiting game for me.
I too have looked to see what other tests they do to tell you're Diabetic the above two sets of the above two glucose ones are routine (I live in Scotland so don't know if it's different elsewhere).
I don't personally understand the GTT test to be honest. I've never been offered it and I've never asked. Through self testing I know how my glucose changes before and after eating.