Different sources will give you different values for the range.
Wikipeidia
http://en.wikipedia.org/wiki/Diabetes_in_cats
home testing). For general guidelines only, the levels to watch are approximately:
mmol/L mg/dL(US)
<2.2 <40 Readings below this level are usually considered hypoglycemic when giving insulin, even if no symptoms of it are seen. Treat immediately
2.2-7.5 40-130 Non-diabetic range (usually unsafe to aim for when on insulin, unless your control is very good). These numbers, when not giving insulin, are very good news.
3.38-6.88 61-124 This is an average non-diabetic cat's level, but leaves little margin of safety for a diabetic on insulin. Don't aim for this range, but don't panic if you see it, either. If the number is not falling, it's healthy.
5 90 A commonly cited minimum safe value for the lowest blood sugar of the day
5.5-10 100-180 Commonly used target range for diabetics, for as much of the time as possible.
7.8 140 According to the American Association of Clinical Endocrinologists (AACE), threshold above which organ and pancreatic damage may begin in humans.
<13.33-15 240-270 Feline Renal threshold for glucose, when excess glucose from the kidneys spills into the urine and roughly when the cat begins to show diabetic symptoms. See Hyperglycemia for long-term effects of high blood glucose on cats.
16.7 300 Approximate maximum safe value for the highest blood sugar of the day, in cats, to avoid neuropathy and complications. Some cats can go on long-term at this level or higher, but there will be side effects eventually. Check for ketones.
>20 >360 Check for ketones frequently, be sure you are giving insulin. Cats are much more resilient than dogs or humans at these high levels; nevertheless, the blood sugar should be lowered. The cat can feel any of numerous ill effects both short and long-term, see hyperglycemia for details.