Widal test is used for detection of specific antibodies produced in response to the stimulation by specific antigen of Salmonella ﴾group﴿
Widal Test Results
The organism Salmonella typhi is responsible for causing Enteric ﴾typhoid﴿ fever is a systemic disease characterized by fever and abdominal pain, loss of appetite, transitory bacteraemia, round or oval‐shaped ulcer over the solitary lymphoid follicle of ileum and the smooth peritoneal surface of Peyer’s patches etc.
The organism possesses the ‘O’ antigen on the cell wall and ‘H’ antigen on its flagella, which then the host body generates immunospecific antibodies to prevent the effect of corresponding antigens.
On the other hand, paratyphoid fever or typhoid fever caused by Salmonella paratyphi A or Salmonella paratyphi B is characterized by a milder course of the disease.
These organisms also contain somatic ‘O’ and flagellar antigen which is termed as A﴾H﴿ and B﴾H﴿ respectively. The Other Organisms of Salmonella species like Salmonella Typhimurium are also responsible for causing food poisoning, or the Arizona group causing fetal infection to have similar antigenic properties. The dead bacterial suspension of Salmonella carries specific ‘O’ and ‘H’ antigens. This will react with immunospecific antibodies, which may be present in the patient serum sample and agglutinate the antigen to produce precipitation or clumps on the slide. A fresh serum sample is preferred for the same. In case of any lag, the sample should be stored at 2°C to 8°C away from direct light. However, the test is to be performed within 24 hrs. of collection of the sample.
Widal Test Process By Two Methods
A. Rapid slide Test AKA Widal Screening Test
- Clean the glass slide provided in the kit and wipe it properly.
- Place a drop of undiluted serum that has to be tested in each of the first four circles ﴾1‐4﴿.
- Add one drop of antigen O, H, A﴾H﴿ and B﴾H﴿ in circles 1, 2, 3,4 respectively.
- Mix the contents of all circles with a separate stick and spread them to the entire circle area.
- Now rotate the slide for a minute to observe for agglutination.
- If agglutination or clumps is visible within one minute, then proceed for quantitative estimation.
B. Quantitative Slide Test
- Clean the glass slide supplied in the kit and proceed further as instructed.
- Take glass slide and prepare dilution of 1:20, 1:40, 1:80, 1:160, 1:320 On circle.
- After preparation of dilution mix and observe agglutination.
- Repeat the above procedure for visible agglutination.
- Titre is the highest dilution observed in the rapid slide screening test, which gives visible agglutination.
Interpretation of Result
A. Rapid slide Test or Widal Screening Test
Granular agglutination in case of Salmonella ‘O’ and flocculating agglutination in case of Salmonella H or A﴾H﴿, or B﴾H﴿
Indicates a positive reaction.
Indicates a positive reaction.
B. Quantitative Slide Test
A diagnostic titre of 1:80 suggests a positive reaction.
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