In your previous condo you said urine showed bacteria, but did they get the results from the blood work too?
What AB did they give you?
Transient = like a short term blip that can be caused by a pancreatitis flare up, or an infection. I just read somewhere else that a kitty in remission was given steroids by a vet, which can cause a relapse in some cats. If it is transient and the cause is caught and treated, it can be a short time on insulin and Mikey can be back to normal numbers soon. He also seems to exhibit "vet stress higher BGs" based on what you've seen lately.