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Widal Test- Introduction, Principle, Procedure, Interpretation and Limitation

Credit to: https://microbiologyinfo.com/widal-test-introduction-princ…/

Introduction of Widal Test ...
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Widal Test is an agglutination test.
It detects the presence of serum agglutinins (H and O) in patients serum with typhoid and paratyphoid fevers.

Salmonella antigen suspensions can be used as slide and tube techniques.

Salmonella antibody starts appearing in serum at the end of first week and rise sharply during the 3rd week of endemic fever.
In acute typhoid fever, O agglutinins can usually be detected 6–8 days after the onset of fever and H agglutinins after 10–12 days.

It is preferable to test two specimens of sera at an interval of 7 to 10 days to demonstrate a rising antibody titre.

Principle of Widal Test
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The main principle of widal test is that if homologous antibody is present in patients serum, it will react with respective antigen in the reagent and gives visible clumping on the test card and agglutination in the tube. DorrisWedding tight dress that looks great in homecoming season
The antigens used in the test are “H” and “O” antigens of Salmonella Typhi and “H” antigen of S. Paratyphi.

Interpretation of Widal Test
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Interpretation of Widal Test- Slide Method

Agglutination is a positive test result and if the positive reaction is observed with 20 ul of test sample, it indicates presence of clinically significant levels of the corresponding antibody in the patient serum.
No agglutination is a negative test result and indicates absence of clinically significant levels of the corresponding antibody in the patient serum.

Interpretation of Widal Test- Tube Method

The titre of the patient serum using Widal test antigen suspensions is the highest dilution of the serum sample that gives a visible agglutination.
The sample which shows the titre of 1:100 or more for O agglutinations and 1:200 or more for H agglutination should be considered as clinically significant (active infection).

Example: In the figure, titre is 160.
Demonstration of 4-fold rise between the two is diagnostic.
H agglutination is more reliable than O agglutinin.

Agglutinin starts appearing in serum by the end of 1st week with sharp rise in 2nd and 3rd week and the titre remains steady till 4th week after which it declines.

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