Although it would be good for your doctor to know you smoke weed, no even if they find THC in your blood, theres nothing they can do about it..
This is too funny because I was wondering the same thing. I had bloodwork and a urine test done in December when I used to smoke everyday, but they never said anything about finding THC in my urine or blood. They have to do a specific drug test for that and your not going to the endocronologist to get a drug test done, they are just checking if everything is good diabetes-wise, such as if you have sugar or blood in your urine. Don't worry, they wouldn't do anything anyways even if they did find something which they won't.