Correct option is B
Explanation-
The Widal test is a serological test used for diagnosing typhoid (enteric fever). It detects the presence of antibodies (agglutinins) in the patient’s serum against the O (somatic) and H (flagellar) antigens of Salmonella typhi and Salmonella paratyphi. In this test, when the patient's serum is mixed with antigen suspension, visible clumping (agglutination) occurs if antibodies are present.
Type of reaction: The reaction seen is agglutination (clumping of particles due to antibody-antigen reaction). Therefore, the Widal test is an example of an agglutination reaction.
Incorrect options-
Option a : Precipitation reaction
In precipitation, soluble antigens react with antibodies to form insoluble complexes that precipitate.
Example: VDRL test for syphilis.
Option c : Complement fixation test
In this test, complement proteins are used to detect antigen-antibody reactions indirectly.
Example: Detection of some viral and parasitic infections (e.g., CFT for syphilis, viral infections).
Option d : Immunofluorescence detection
Uses fluorescent-labeled antibodies to visualize antigen-antibody reactions under a fluorescence microscope.
Example: ANA test, viral infections, certain autoimmunological tests.
So, the correct answer is option b - agglutination reaction.
