IgG and IgM are used to detect whether a person has produced antibodies after being infected with a virus and what type of antibodies they are. If the IgG antibody is positive, it indicates a past, previous infection with a pathogen, while a positive IgM indicates whether the patient is currently, or not currently, infected with a pathogen. Therefore, if a patient’s test indicates positive IgG antibodies and negative IgM antibodies, it means that the patient has had a past, previous infection with a virus or other pathogen. If both antibodies are positive, the patient is currently infected with a pathogen.