The IgG, IgA, and IgM tests measure the levels of different antibodies in the blood to assess the functioning of the immune system. IgG is the most common antibody in the blood and is responsible for long-term immunity. It is produced after initial exposure to a pathogen (such as a virus or bacterium) or following vaccination. IgM is typically the first antibody produced in response to a new infection and indicates an acute or recent infection. IgA is mainly found in mucous membranes (such as the respiratory and gastrointestinal tracts) and in body secretions (like saliva and tears), where it helps prevent pathogens from entering the body. These tests are used to diagnose immune deficiencies, identify current or past infections (such as COVID-19 or measles), evaluate response to vaccines, or assess autoimmune diseases (like lupus). Abnormal levels of these antibodies may indicate chronic infections, allergies, or immune system disorders. Interpretation of the results should be done in the context of the patient’s symptoms and other laboratory tests.