Febrile Antigen tests are used in the detection of antibodies produced in certain febrile diseases such as salmonellosis, brucellosis and rickettsial diseases. Febrile antigen tests are serological applications of the classical Widal reaction for the diagnosis of typhoid fever and the Weil-Felix test reactions where antigens prepared from Proteus organisms are used to detect related rickettsial antibodies.
Serological diagnosis of patients suspected of having infectious diseases characterized by persistent fever is dependent upon demonstration of an agglutination reaction between the appropriate antigen and antibody.
The natural response to the invasion of pathogenic organisms is the production of antibodies. This immune response is highly individualized and in addition to the host’s physiological status and genetic capabilities, a number of other factors are involved in the production of antibodies to the particular stimulus. These include the antigenicity of the organism, the total amount introduced to the host and the route of introduction, and whether the host has had previous exposure to the organism. These factors will determine the rate of antibody formation, the amount of antibodies produced and their persistence in the circulatory system.
The patient’s serum is tested directly for specific antibodies by either slide or tube agglutination test. These tests are qualitative and semi-quantitative. The rapid slide test is used primarily as a screening procedure especially useful when large numbers of sera must be examined. The tube test should be used to confirm positive results obtained by the slide test.