widal test

WIDAL TEST

Defination: a test involving agglutination of typhoid bacilli, when they are mixed with serum containing typhoid antibodies from an individual having typhoid fever; used to detect the presence of Salmenolla typhi and Salmonella paratyphi.

Widal test is a serological test for enteric fever or undulant fever.
In case of Salmonella, agglutination antibodies against antigens O-somatic and H-flagellar in blood.
In case of Brucellosis, only O-somatic antigen is used.
It is not accurate method, since patients are not exposed to other bacteria (eg: Salmonella enteritidis, Salmonella typhimurium) these induce cross-reactivity; people have antibodies against these enteric pathogens, also react with antigens in the widal test, causing false- positive result.