I would ask you why you are worried about being forewarned? It is what it is, and an OGTT at home won't change things. Why not just ask for the HbA1c when you see your doctor and accept what it tells you.
Home OGTT
The solution I used when I did my home OGTT was Rapilose, as DCUKMod said. It is a drink that contains exactly 75g of glucose and nothing else at all. You just pour it into a glass and drink it in 5 minutes. It is used in many surgeries now that Lucozade has gone reduced sugar.
https://www.gpsupplies.com/rapilose-ogtt-glucose-solution-300ml-pack-of-1
You do need to be organised when you do the test. You should also eat 130g carbs a day for 3 days beforehand or the test may be inaccurate. You will need to pick a morning when you have nothing else to do. Fast overnight, no food. Test your fasting BG. Drink the liquid. Sit quietly for at least 2 hours - no food, no water, no moving about, no smoking, no stress or disturbances. Then you test at whatever frequencies you chose, but as a bare minimum at 1 hour and 2 hours after finishing the drink. If you want extra information you can test half hourly and keep going after the 2 hour mark. You need to record all these readings with the times.[/QUOTE
Thanks Bluetit, Is it actually 'what it is' if going low carb lowers the HbA1c? Would you say that it wouldn't be an accurate reading and would I just be delaying the inevitable? I'm only trying to keep off the radar and is this a good idea or not? Is it that just being a prediabetic is little different to being full T2, I need to sort my carbs and can't allow things to slide?
I've never really got my head round this carb counting exercise, it all sounds technical but having said that I do trim back on the obvious and fill up on leafy vegetables. It's quite possible that I'm worrying unnecessarily but I do feel that I've let things slide since Christmas so maybe I should just bite the bullet as you say and ask for the HbA1c.
Incidentally my son [aged 49] has Hypothyroidism and was warned at his last check up that his HbA1c was also 43. He doesn't live in the UK so I gave him some tips on low carbing [who am I to talk!] and he later went for another test to another dr where he sent me the result of 'post prandial 7.5 - test method Hexokinase.' I asked him what that was and he said they had given him breakfast, he'd waited 2 hrs then was re-tested. He said the 'breakfast' was a croissant and a glass of orange juice !! I thought he was joking but he was quite serious.