Serological tests are laboratory procedures used to detect and measure the presence of antibodies or antigens in a sample, usually blood serum. These tests help diagnose infections, autoimmune diseases, and allergies by identifying the immune response to specific pathogens or substances. Common types of serological tests include enzyme-linked immunosorbent assay (ELISA), Western blot, and immunofluorescence. They are essential tools in clinical diagnostics, epidemiology, and research, providing valuable information about a person's immune status and exposure to various diseases.