You are TB negative <5mm. Your body does not have TB bacteria or the antibody. You do not need X-ray.
You are TB positive. Your have dormant TB bacteria in you lung. You have 10% of the change to have active TB later in your life. You need take 10 month of medicine, which will decrease this possibility to zero. All Chinese were immunized against TB as child. However, the effectiveness of immunization is disputable or doubted by many doctors. The immunization will generate antibody in your blood. Then you are TB positive.
You had previous TB, treated and fully recovered. Just tell the doctor this. You need an x-ray done. Most likely, you will be referred to local health department. They will do a culture test. A negative result means you are fine. It causes no trouble for you GC application.
I have all the situations for me and my family. Our 485 just got approval.