It is my opinion, but if I were you...

1. If I am worrying about the medical exam sheet, I will find another doc, just safe for I-485 application.

2. If this doc give me a safe result sheet and I don't want to change a doc, plus I am sure I don't have TB, then I will get the drugs, but won't take it.In this case, I know I have to see the doc for follow-up.

3. People should understand that it is doc's protocol to give you drugs even they don't have evidence show you have TB--they HAVE TO give your the preion.

4. Usually the drugs are INH and rifampin.... those drugs have some side affects, especially for long term usage (usually needs 6-9 months under protocol).

5. Don't worry about follow-up, once you are TB positive, they should not give you skin TB test again,usually they just ask you to make sure you don't have subsequent TB sympotom (cough,low fever, weight loss,night sweats...). They will follow up you for half to one year.