Widal Test (Slide Test)

The Widal test is a serological agglutination test used in clinical/diagnostic laboratories to diagnose enteric fever (Typhoid or Paratyphoid fever). This test measures the amount of agglutinating serum antibodies generated against Salmonella Typhi and Paratyphi A, B, and C&’s O (somatic) and H (flagellar) antigens. This test is widely utilised as a primary diagnostic technique for detecting enteric fever all
over the world.

Antibodies against the bacterium’s O and H antigens are common in the serum of a patient with enteric fever who has been infected with Salmonella. After 6-8 days of infection, antibody levels against these antigens will peak. The serum is collected from the suspected patient’s blood and allowed to react with Salmonella Typhi O and H antigens, as well as Salmonella Paratyphi AH and BH antigens. If anyantibodies are present in the serum, they agglutinate antigens specifically and cause apparent clumping.