Serology is the scientific study of serum and other body fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum.[1] Such antibodies are typically formed in response to an infection (against a given microorganism),[2] against other foreign proteins (in response, for example, to a mismatched blood transfusion), or to one's own proteins (in instances of autoimmune disease). In either case, the procedure is simple.[citation needed]