Infections, tummy bugs, viruses and things like pain and inflammation, may all send blood glucose high.
A couple of Xmases ago I went to a party and came home with food poisoning. Fun fun fun.
The fascinating thing was tracking my blood glucose, it was up and down like a... um... trying to think of a delicate description, and I can't. Suffice it to say that my blood glucose went more than twice as high as usual, then dropped like a stone, then up, then down, for about 18 hours. Not in time with the bathroom visits, but still as regular as clockwork.
In fact, it was the blood glucose settling down that told me I was getting better. The other symptoms improved later.
Hope that helps.