Serological tests may be performed for diagnostic purposes when an
infection is suspected, in rheumatic illnesses, and in many other
situations, such as checking an individual's blood type. Serology blood
tests help to diagnose patients with certain immune deficiencies
associated with the lack of antibodies, such as X-linked
agammaglobulinemia. In such cases, tests for antibodies will be
consistently negative. There are several serology techniques that can be
used depending on the antibodies being studied. These include: ELISA,
agglutination, precipitation, complement-fixation, and fluorescent
antibodies.