What test indicate old or previously treated infectious diseases? antigen, toxin, protein, anti-body..?

Extremely complicate: It depends on what disease. Syphilis for example has several tests..Rpr using a reagin looking for an antibody to the spirochete. Clostridium difficile looks for toxin a and b. Hiv western blot looks for HIV envelope proteins. Igm indicated a more recent infection while igg a longer time interval. It is not as simple as it seems defining old vs new..Tb for instance is a good example.