Hey Fi!
Surgery always carries risk, but the risks go up significantly if your BG is high. If you need an emergency op, they will weigh the risks of doing the op with high BG against not doing it. As your op is not an emergency, they might decide the risks of operating outweighs the benefits of surgery. If that is the case, they will tell you to get your BG under control before they operate. As you know, 19.3 is way too high. It increases the risks of strokes and other serious problems while under anasthaetic. I wouldn't be at all surprised if they postpone your op until your diabetes is controlled. If they do, it will be for your own good, so try not to be angry/upset. It is better to wait than risk your health if that's what they decide. Your GP should know this and should be helping you manage your diabetes. Personally, I would go back to your GP and ask to review your diabetes management.
Good luck
Smidge