Hi Kath! From what I've seen it's not unusual for OTJ kitties to 'slip', often because they're stressed by illness, a move, something going on in the home, or high-carb food is being given, etc. I think it's more common in cats that were on insulin long-term. And of course it depends on circumstances - if a cat was diabetic because of being on steroids or whatever, when the cause is removed and the diabetes is brought into remission they're much less likely to need insulin again. Very often a cat can go OTJ again, especially if it's caught quickly, so continued occasional testing is important. I think the standard frequency is monthly (maybe someone else knows more about this?), but personally I wouldn't go less often than weekly.