If your reading of 7.2 mmol/L (Plasma) was done after a period of fasting for the full 12 hours (i.e. Morning Blood Test) then its crossed the diabetic threshold, though your HbA1c reading, if this was taken at the same time would indicate good average blood/glucose control. This may be why they are checking further and asking you to undertake a GTT test to see how well you are coping a dealing with a specific quantity of Carbohydrate after drinking it (Usually it's 100ml of Lucozade).
Before the GTT is undertaken you should ensure that your lifestyle hasn't altered and that you are free from any colds or infections and in good health, otherwise this can effect their final results.
They usually prefer to extract the samples of blood from a vein in the crook of the arm over a time period, having first taken your morning fasting blood glucose level as the reference and then giving you the Lucozade drink.
From all the results of the various samples that are taken, they can then see how well or otherwise you are coping a digesting a fixed volume of glucose loading, and from the results thay can decide if you are diabetic or not. The difficulty is where someone falls between the two limits, and depending where that are in relationship to the upper and lower threshold (The Pre-diabetic Stage) they might decide to conduct further testing in the months or years to come.
If this should prove to be in your result, then you need to take this as a warning, as changing your lifestyle through modest exercise and a revised diet can in most cases reverse the pre-diabetes and save you from eventually becoming a full time member of the 'Diabetes Club'
Best of Luck with your GTT - Lazybones
