This test, in your case, is used to detect auto antibodies, that is, antibodies elaborated by the body against its own tissues, which occurs in a category of diseases known as auto immune diseases, a group of disorders that result from an aberration in the normal function of the immune system. In the case of suspected systemic lupus erythematosus (SLE), such test aims at detecting an antibody called anti nuclear antibody (ANA). The control is not the main purpose of the test, it's only a sort of a reference for the test makers to ensure test accuracy and that the result is reliable, so it is expected to be positive.