Serology is the scientific study of blood serum and other bodily fluids. It involves the analysis of antibodies, which are proteins produced by the immune system in response to an infection or other foreign substance in the body. Serology tests can be used to detect the presence of antibodies in the blood, which can help diagnose infectious diseases such as HIV, hepatitis, and Lyme disease. Serology tests can also be used to determine whether someone has been vaccinated against a particular disease. Additionally, serology can be used to test for autoimmune disorders, which occur when the immune system mistakenly attacks the body's own tissues. Serology is an important tool in both diagnosing and monitoring infectious and autoimmune diseases.