HIV

Human immunodeficiency virus targets immune cells and, without effective treatment, progressively weakens immune function. Early infection may cause fever, rash, fatigue, diarrhea, sore throat, myalgia, headache, or lymphadenopathy, but symptoms are neither sensitive nor specific. Chronic infection may remain clinically silent for years. Testing, rather than symptoms alone, establishes the diagnosis. Effective antiretroviral therapy suppresses viral replication, preserves immune function, and allows people living with HIV to have long and healthy lives. A screening assay is designed to identify specimens that may contain evidence of HIV. A reactive screening result is therefore a preliminary positive, not a diagnosis. Canadian laboratories use fourth-generation combination assays that detect HIV p24 antigen and antibodies to HIV. P24 antigen can become detectable before the antibody response, which improves recognition of early infection compared with an antibody-only test. Think of screening as a smoke alarm: it identifies a signal that needs resolution but does not establish the source. A reactive screen cannot by itself distinguish HIV type, acute infection, established infection, or a false-reactive result. The predictive value of a reactive result also depends on...