"It is not unusual for insulin requirements to change suddenly even after a long period of stability. "
Dose adjustment should be based on the clinical response and the results of serial blood glucose samples and not just a single sample. Ideally a blood glucose curve should be made before the insulin dose is changed.
Urine glucose and ketone monitoring can be used to check whether a blood glucose curve should be made, it should not be used alone as a basis for dose adjustment.
Changes in dose should be made after a period of adjustment to a particular dose or regime. In cats the dose can be adjusted as infrequently as after 1-3 weeks on a particular regime. Increases of 1IU per injection are recommended.
