Complement fixation test (CFT) for mycology

 

The test is based on the Laboratory Branch Complement Fixation (LBCF) Test procedure. The principal of the CF test is that antibodies present in patient sera, when mixed with the corresponding antigens will "fix", or bind, complement (a component of fresh serum). his "fixation" of complement is determined by using an assay system consisting of sheep red blood cells (SRBC) sensitized with anti-SRC (hemolysin) and measuring the percentage of lysis of the SRBC (unbound complement initiates lysis). If all complement has been "fixed" the indicator SRBC's will not be lysed.

 

 

1. Complement (C) is irreversibly bound (fixed) by certain classes of antibody-antigen complexes(certain classes of antibodies do not fix the complement). The degree of fixation is governed by the relative concentration of antibody or antigen

 

2. The lysis of SRBC that have been sensibilized with hemolysin is dependent upon the presence of unbound complement.

 

THe CF test is interpreted as follows : 

• Antibody present=no hemolysis
• Antibody absent=hemolysis

Patient sera should be tested with each of the antigens , since there is some overlap in the antigenicity between the various fungi and the symptoms of the diseases are very similar. Higher CF titers are usually observed on patient sera when they are tested against the same antigen as the etiologic agent of their infections.

 

 

 

These antigens are prediluted to the optimal concentration for use in the LBCF procedure and are ready for use as supplied. The optimum dilutions for these antigens have been determined by "box-titration" against sera from proven cases of the mycoses with known titers. The optimmally diluted antigens are available as follows :

 

 

The positive controls arefrom hyperimmunized goats. Each positive control should give a 1:32 titer (+/- 1 dilution) with its optimally diluted homologous antigen. The negative control should be negative in the CF test with all antigens.