I have never been tested for TB at my CF clinic...but my sister-in-law gets tested often because of her job. I thought it was very interesting that perhaps getting tested too often could show a false positive, because after she was tested at work, she didn't believe the "negative" (i have no idea why), so she went to a Patient First and asked for the test, and it showed she had latent TB, so now she has to take a medication once daily for six months, with a blood test every two weeks because of this med's effect on the liver. And it all could just be because she had two tests back to back!