They don’t need to be, but if your blood sugar is high, you will heal more slowly and be at greater risk of infection.
So the best thing you can do to protect yourself is to get your diabetes under control before you have surgery, if that’s an option. Obviously, some surgeries cannot be delayed. Anything involving the removal of cancerous tissue comes to mind as a good example; while a hip or knee replacement could probably wait a few months.
If your blood sugar control is poor and you’ve never been able to manage it, here are some things to consider with your doc before you go under the sterilized knife: if you are opposed to taking insulin, maybe you should re-think that, even as a temporary measure. You can also modify your diet. Even if you’ve never been able to do this in the past, taking it on as part of your pre-op preparations may not seem as daunting as a for-the-res-of-your-life change.
You should also look at ramping up the frequency of your blood sugar checks, just to make sure you have a clear picture of what’s going on in your body.
Also make sure your medical team is in good communication with your surgical team. You’ll need to have a plan in place for when to stop your diabetes medications before the surgery and when to start them again afterwards.