PPD stands for purified protein derivative. I work in healthcare as well and have to have this annual test done. Over the last few years I have a reaction to the PPD serum itself, not a postive TB reaction. No one has been able to explain this to me as to what it is I am reacting to in the serum, why I am reacting to it, or what to do about it. My arm gets a little swollen, turns very red and sometimes bruises up, with a lot of itching and discomfort. This generally lasts about 2 weeks after having the original PPD done. The first time this happened (about 3 years ago)I ended up going to see the ER physician at my facility and he said it was a serum reaction, not TB; the OR nurse (who administered it) said this is getting to be a more common thing. I haven't yet found any real helpful information on it.