Widal test

Definition

The Widal test is a serological assay used to diagnose enteric fever, particularly typhoid fever, by detecting agglutinating antibodies against Salmonella antigens in the patient's serum.

5 Must Know Facts For Your Next Test

1. The Widal test detects antibodies against O and H antigens of Salmonella typhi and Salmonella paratyphi.
2. A significant rise in antibody titer between acute and convalescent samples is considered indicative of infection.
3. False positives can occur due to previous vaccination or infection with related bacteria.
4. Proper interpretation requires knowledge of baseline titers in the local population.
5. Agglutination typically occurs within minutes to hours when specific antibodies are present.

Review Questions

• What are the main antigens detected by the Widal test?
• Why might a false positive result occur in a Widal test?
• How is a significant rise in antibody titer interpreted in the context of diagnosing enteric fever?

Related terms

Agglutination Assay: A laboratory method used to detect the presence of specific antigens or antibodies through their ability to form visible clumps.

Serology: The scientific study or diagnostic examination of blood serum, especially with regard to the response of the immune system to pathogens or introduced substances.

Typhoid Fever: An infectious disease caused by Salmonella typhi, characterized by prolonged fever, headache, nausea, loss of appetite, and constipation or diarrhea.