When he was at Michigan State on August 20 for surgery, his glucose was 320-but that was after he had been in the car for over an hour and at MSU for over an hour before they drew blood. So, it could have been elevated due to stress. But the surgeon was concerned that he was pre-diabetic. The fructosamine test was also high.
The regular vet thought the elevated glucose was due to stress because whenever he's had blood drawn at the regular vet's office-because it's close to home and he has less time to be stressed-the glucose has been normal.
And it has nothing to do with how well the kidneys are or are not functioning (in his case, at this time.) The regular vet said that when glucose gets above 250-280, that the "extra" will spill over into the bloodstream regardless of kidney function.
However, we had also been feeding him a different cat food for the two weeks between surgery and the blood recheck which could have affected the outcome. The food was Fancy Feast Classic which has no gravy, therefore, fewer carbs. And we were also feeding Purina Naturals grain free food which supposedly has fewer carbs. That could have caused the difference. We will know more when we recheck the fructosamine at the end of the month.
When kidney function has declined, it is possible that sodium, glucose, magnesium, and many other blood values will increase. If all blood values are normal except glucose, then it is possible that a cat is diabetic. If there are spikes in glucose, then the cat could be pre-diabetic. And while the fructosamine test is suppose to be the standard for determining if the cat is diabetic, it acts as a historical aggregate of glucose levels. So, even when glucose is falsely elevated due to stress, the fructosamine will reflect that history.