I just finished the medical examination for I485. What I know is if the TB test is negative, it will be valid for one month. This is my situation. If it is postive and you take some treatment, you don't have to do TB test any more. This is the situation of my colleague. But if you are positive on TB test, and negative TV on X-ray, I don't know what will happen. You can bring all the records to medical center and see what they will tell you.