Complement Fixation test is: September 2005

Ans. C: Wassermann reaction The complement fixation test (CFT) was extensively used in syphilis serology after being introduced by Wasserman in 1906. However, there is now a trend to replace the CFT with the simple flocculation tests. Although CFT is considered to be a relatively simple test, it is a very exacting procedure because 5 variables are involved. In essence the test consists of two antigen-antibody reactions, one of which is the indicator system. The first reaction, between a known virus antigen and a specific antibody takes place in the presence of a predetermined amount of complement. The complement is removed or "fixed" by the antigen-antibody complex. The second antigen-antibody reaction consists of reacting sheep RBC with haemolysin. When this indicator system is added to the reactants, the sensitized RBCs will only lyse in the presence of free complement. The antigens used for CFT tend to be group antigens rather than type-specific antigens. In order for the CFT to be set up correctly, the optimal concentration of haemolytic serum, complement, and antigen should be determined by titration. The Wassermann test is no longer in use.