I have a question and hope someone can point me in a direction of more information. My facility is in the process of considering switching from regular yearly PPD testing to two-step testing. I understand the theory behind two-step testing to be that by testing again a week or two later, that any late reaction caused from the first PPD test will be picked up when given a second PPD test. I've searched the internet, including the CDC and WHO and cannot find any information other than that some organizations "recommend" two-step testing. Does anyone have any concrete info they could share - or point me in the right direction to find it? Much thanks.