This was a post
@Nederland posted. She has a lot of experience with Caninsulin:
"In the Netherlands we have lots of experience with caninsulin. I've been moderating a forum for diabetic cats for 18 months now, and have learned quite a bit (not yet all, though).
The lowest point with vetsulin (if it is the same as caninsulin) is between +3 and (sometimes) +6, but mostly around +4 or +4.5. Caninsulin is designed tot act fast and has a first peak around the mentioned +4, and after that a second peak at +6/+7. The numbers tend not to rise back quickly, but stay in the 'low' numbers for a couple of hours. Not all cats do that second peak (peak as in peak of the working of the insulin).
Dogs have the lowest point around +6, and some vets think cats are dogs. They are not. A test of a cat 6 hours after the shot is NOT a good base to make decisions on about the dose.
But first needs to be determined whether the dose is too high or too low. If there is a Somogyi effect, the drop will be very fast, and the rising again will also be very fast, to very high numbers. If the 3 units was too much for a longer time, the numbers will hardly or not drop at all (insulin resistance).
You home test apparently. Could you please test the preshot value, a +2, +3 and a +4?"
Her suggestions on testing are very important to get a good idea of how fast and well the insulin is working