The night before you go to have the blood drawn, they will tell you nothing to eat or drink after midnight (water is OK). You'll go in and they'll draw blood from a vein, and depending on what tests the doctor orders to check the glucose levels in your blood they may take one or two vials. Legally they cannot do a drug test without your permission. If you're under 18, unless you've done something silly and made your parents suspicious enough to want to do a test, you should be good....and besides that, if they're thinking you're a diabetic, they probably aren't worried about doing a drug screen, they probably just want to figure out what's wrong with you.

Oh yea....they also might have you pee in a cup to test your urine for glucose and protien....don't freak out, it's not for a drug test, just to check and see if any glucose or protien is spilling over into your urine...