I have to have regular blood tests for my hypothyroidism and I make sure I drink a litre of water 10 minutes before I leave home to have the test. I have had a full auxilllary clearance in one arm, so I don't let them take it out of that arm, and haven't had a problem. The only time had a problem was when I had a trainee phlebotimist so now I request a fully trained operator. I also hate having the test, but I just have to put up with it, but has been ok, I just get them to take blood out of the arm that has had the less intervention.