complement fixation n the process of binding serum complement to the product formed by the union of an antibody and the antigen for which it is specific that occurs when complement is added to a mixture (in proper proportion) of such an antibody and antigen
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the binding of complement to the complex that is formed when an antibody reacts with a specific antigen. Because complement is taken up from the serum only when such a reaction has occurred, testing for the presence of complement after mixing a suspension of a known organism with a patient's serum can give confirmation of infection with a suspected organism. The Wassermann reaction for diagnosing syphilis is a complement-fixation test.
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fixation of complement the consumption of complement upon reaction with immune complexes containing complement-fixing antibodies; this is the basis of complement fixation tests, two-stage procedures in which heat-inactivated antiserum (or antigen) is reacted with the test material in the presence of a known amount of complement. If the homologous antigen (or antibody) is present in the test material, complement is fixed. Then sheep red blood cells and antisheep erythrocyte antibody are added; lack of hemolysis indicates complement fixation, i.e., a positive test result. Quantitative results are obtained by determining the highest dilution of antiserum or test material that gives a positive reaction. Called also Bordet-Gengou phenomenon or reaction.Medical dictionary. 2011.