Huni98 it does makes sense if you think about it because the forms the doctor has to fill in ask for the reaction in mm. If the doctor doing your paper work checks the box that says ppd taken and positive and doesn't put the reaction results (because obviously he didn't take your test and is only taking your word on its positive reaction so how would he know what your reaction was) then the USCIS will want to know what the reaction was because apparently the more mm the higher risk you are or whatever. If they check the ppd not taken box (as they should because even if you did take that test before and it was positive, they did not themselves take it and did not see with their own eyes that it was positive) then the USCIS will want/request it to be taken and the reaction recorded. They basically want the doctor to take care of both questions that deal with the ppd- 1) was it taken, and, if positive give the reaction and 2) was an x-ray taken and what were the x-ray results.