HIV (Human Immunodeficiency Virus) serology tests detect antibodies and/or antigens produced in response to HIV infection. Modern combination tests (4th-generation HIV assays) simultaneously detect HIV-1 and HIV-2 antibodies and the p24 antigen, allowing detection as early as 2-4 weeks after infection.

HIV attacks and progressively destroys CD4+ T lymphocytes, which are critical for immune defence. Without treatment, this leads to acquired immunodeficiency syndrome (AIDS), characterised by opportunistic infections and malignancies. With modern antiretroviral therapy (ART), people with HIV can maintain near-normal immune function, normal life expectancy, and an undetectable viral load (which also means non-transmissible).