A. The high sugar levels are not be worried about as most cats have elevated blood sugar levels as a result of stress when they are at the vet. the high temperature and high WBC indicate severe infection. this could be a severe gastroenteritis, pancreatitis, hepatitis or foreign body in the intestines..
I assume the vet gave him an anti emetic injection and antibiotics? if so you need to wait and offer him some gastrointestinal food about 2 hours after that injection, hopefully the appetite will start coming back soon.
If he is not better by tomorrow, take him back to the vet.
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