This is a valuable bit of information about steroids and blood sugar sent to me by a list friend who is an MM sufferer and MD.
Transient elevations of the blood sugar do very little harm, diabetes is a long term disease. You have to have persistent elevations of your blood sugar over decades (yes decades) to see real end organ damage. An occasional spell of elevated BS is of very little concern. That said, I am in no way supporting a life style of not watching your blood sugar, good control of the BS is important. The scale is important too, in other words, a BS of 125 is more of a flag, a BS of 350 is out of control and needs action because of the related effects (vision, kidney, dehydration etc).
There is a test I would highly recommend, the HB A1C. This is a marker that does NOT respond to rapid changes in BS, but will drift upward if the BS is persistently elevated. If a patient comes in with a BS of 275 but is normal all other days, the A1C will be normal. We use it to monitor long term control. On the other side of the equation, if a patient has an elevated A1C, that means he/she must be out of control most of the time even if they are normal the day of the office visit. If you are having intermittent elevations of your blood sugar, a HB A1C is a good test to run. A normal value for the A1C would be very reassuring. It is a cheap test and widely available.