It's a fructosamine test (not glucosamine).
I would not want my cat in the 300s without insulin for overly long -- certainly not weeks. If there's an underlying infection, the high numbers plus an infection increases the risk for your cat developing diabetic ketoacidosis (DKA). Not enough calories also can contribute to DKA developing. DKA can be a life threatening emergency. Your observation that Nala isn't acting like herself is also a concern.
Some of the time, examining a cat's teeth when the cat is awake doesn't allow for a good look at the back teeth which is where plaque develops. I think you're making too many assumptions. (Sorry!)
I would not want my cat in the 300s without insulin for overly long -- certainly not weeks. If there's an underlying infection, the high numbers plus an infection increases the risk for your cat developing diabetic ketoacidosis (DKA). Not enough calories also can contribute to DKA developing. DKA can be a life threatening emergency. Your observation that Nala isn't acting like herself is also a concern.
Some of the time, examining a cat's teeth when the cat is awake doesn't allow for a good look at the back teeth which is where plaque develops. I think you're making too many assumptions. (Sorry!)