Normally done about twice a year once you've stabilised but to begin with could be (should be!) more frequent. If you think that's a complicated name, try Glycosulated Haemoglobin, which mouthful they used to have to come out with LOL We just usually abbreviate it to A1c cos it's easier.
To do it, they may either have to take blood from an arm and send it off, or some hospitals now have expensive machines that do it there and then. Wish they all did.