A male patient with the presentation as outlined (fatigue, weight loss, and lymphadenopathy) must be tested for antibodies to HIV. While other antibody tests may be relevant after the primary diagnosis, they must be considered after HIV is ruled out. Ceainly, infectious mononucleosis is a possibility, but its occurrence in this age group is not as frequent as HIV. Patients are tested first by an ELISA screening test. If this test is positive (X2), then a confirmatory Western blot is performed. A Western blot separates the immune response into antibody production for specific components of the virus, that is, envelope, gag, and so foh. Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition