Complement fixation test (CFT)
The fungal antigens and positive controls are used to detect antibodies in patient serum by the complement fixation (CF) procedure to aid in the diagnosis of four specific fungal diseases : Histoplasmosis, blastomycosis, coocidioidomycosis and aspergillosis.
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.
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.