Serology

Serology is the study and diagnostic use of blood serum and other body fluids to detect antibodies, antigens, or immune responses. In medical diagnostics, serologic tests rely on antigen–antibody interactions to identify past or current infections, exposure to a pathogen, or immune status after vaccination. The core principle is that exposure to an antigen stimulates the production of specific antibodies detectable in serum. Tests can be qualitative (positive/negative) or quantitative (antibody titer).

Common techniques include agglutination assays, precipitation reactions, enzyme-linked immunosorbent assays (ELISA), immunofluorescence, and Western blotting. Rapid diagnostic tests and chemiluminescent assays are widely used for practical, point-of-care or high-throughput settings. Serology can also involve testing for antigens rather than antibodies.

Applications are broad. Serology is essential for diagnosing infectious diseases such as HIV, hepatitis B and C, syphilis, and other pathogens; for screening blood donors; and for determining immune status after vaccination. It supports autoimmune disease testing (for example, antibodies such as ANA or rheumatoid factor) and can aid in allergy assessment and transplantation medicine by identifying antibodies against donor antigens.

History and context: serology emerged from the discovery of antibodies and blood typing in the late 19th and early 20th centuries, with milestones including the work of Karl Landsteiner on blood groups and Emil Behring’s development of antitoxins.

Limitations include false positives and negatives due to cross-reactivity or low antibody levels, the window period before antibodies appear after infection, and assay variability. Proper controls and standardization are essential for reliable interpretation. Serum is the standard sample, though plasma can be used for certain tests.