The ELISA (Enzyme-Linked Immunosorbent Assay) test is a common diagnostic method, often used in the context of HIV screening. It works by detecting the reaction between an antigen (such as a specific protein of a microorganism) and an antibody (a protein produced by the immune system in response to an antigen). An enzyme is utilized to make this reaction visible, allowing for the detection of various infectious agents or the antibodies the body produces against them. For HIV, the ELISA test typically screens for the presence of HIV antibodies or antigens in a sample, indicating a potential infection.