I Have Lab Tests Tomorrow And I Know They Will

I have lab tests tomorrow and I know they will take my blood. I'm not sure exactly what they are testing me for but I know they aren't testing specifically for any sort of drugs. They are testing me to see if it's okay for me to take this medication pretty soon. I have to fast and not eat or drink things for twelve hours. I want to smoke weed today and I would have my test tomorrow morning. Is it okay for me to smoke weed?? Will it show up on anything???