Complement fixation (CF) is an immunological test that can be used to detect the presence of either specific antibody or specific antigen.  Complement fixation reagents include Guinea Pig Complement (30-956J), Sheep Erythrocytes (55-401A), and Hemolysin (55-402J). 

The CF test involves two basic principles:

  • Complement is irreversibly bound (fixed) to antigen-antibody complexes. The degree of fixation is governed by the relative concentration of either antigen or antibody.
  • The lysis of sheep red blood cells in the presence of homologous antibody (hemolysin) is dependent upon the presence of complement.


The Complement Fixation test is interpreted as follows:
antigen + serum+ complement + sensitized  sheep red blood cells

  • antibody present = no hemolysis
  • antibody absent = hemolysis


Influenza virus was shown to agglutinate chicken red blood cells (RBC).  Subsequently, a variety of viruses have also been shown to be capable of agglutinating RBC's from several different species.  Virus has been shown to agglutinate red blood cells Chicken Red Blood Cells (30-904J) and Guinea Pig Red Blood Cells (30-957J) in the hemagglutination (HA) assay.  It has also been observed that specific antibody could inhibit hemagglutination which led to the development of the hemagglutination inhibition (HAI) assay.  The HA-HAI capability provides a fast and easy method of quantifying both viral antigen and antibody.  The specificity and sensitivity of the HAI assay is dependent upon the characteristics of the HA antigen and its interaction with antibody, which will vary with the particular virus under test.