ELISA tests are commonly used in clinical diagnostics to detect infections like HIV, hepatitis, and COVID-19. They also play a vital role in monitoring hormone levels (e.g., thyroid hormones), detecting autoimmune diseases (e.g., lupus), and identifying allergens (e.g., food allergies). In research, ELISA is applied to study biomarkers in cancer, neuroscience, and immunology, and to assess the presence of specific proteins or antibodies in samples like serum, plasma, and cell lysates.