Aspergillosis, caused by the filamentous fungus Aspergillus, encompasses a spectrum of diseases that range from mild allergies to severe invasive infections. Accurate diagnosis of Aspergillus infections is crucial for appropriate patient management and treatment decisions. Complement Fixation Test (CFT) stands as a valuable serological technique employed to assess the immune response to Aspergillus antigens and aid in the diagnosis of Aspergillosis.

CFT is an immunological assay that exploits the principle of antigen-antibody interaction, specifically involving the activation of the complement system. The complement system is a component of the innate immune response and plays a vital role in defending against microbial infections. The CFT measures the ability of patient serum antibodies to fix complement components when exposed to Aspergillus antigens.

In the CFT for Aspergillus, patient serum is mixed with a standardized preparation of Aspergillus antigen, usually a crude extract or purified fungal components. The mixture is then incubated, allowing the antigen-antibody complexes to form. Following incubation, a standardized amount of complement is added, and the mixture is further incubated. If patient antibodies specific to Aspergillus are present, they will bind to the antigens, initiating the activation of the complement system. The fixation of complement components can be detected by various methods, such as hemolysis of erythrocytes or the addition of indicator systems.

The CFT for Aspergillus provides a qualitative and quantitative assessment of the patient's immune response to Aspergillus antigens. It aids in the diagnosis of various forms of Aspergillosis, including allergic bronchopulmonary aspergillosis (ABPA), chronic pulmonary aspergillosis (CPA), and invasive aspergillosis (IA). The presence of specific antibodies against Aspergillus in the patient's serum indicates exposure to the fungus and suggests an ongoing or previous infection. The titer or level of antibodies can also provide insights into the severity and progression of the disease.