It is not unusual for your cat’s insulin requirements to change even after a long period of stability. This is most commonly due to:
This is why it is important to continue to monitor your diabetic cat's progress - even after months or years of treatment - and consult your veterinarian if there are sudden changes or if anything unusual happens
You may be asked by your veterinarian to regularly check the glucose (and ketone) concentrations in urine or blood samples. This gives an additional indication of how your cat is doing. Based on these results your veterinarian might decide to do a serial blood glucose curve to determine a new insulin dosage.
You should not change the dose of insulin without first consulting your veterinarian.