How is Widal Test done for Typhoid Fever? | 1mg

Описание: The Widal test is a presumptive serological test for enteric fever. This test measures the titres of antibodies against the bacteria which cause enteric fever.

The Two Types of Enteric fever are:
-Typhoid fever : It is caused by bacteria Salmonella typhi (S. typhi).
-Paratyphoid fever : It is caused by bacteria Salmonella paratyphi A, S. paratyphi B and S. paratyphi C.

What are the Symptoms of Enteric Fever?
Symptoms include:
-High fever
-Stomach pain
-Headache
-Tiredness
-Weight Loss
-Diarrhea or Constipation

What is the basis of Widal Test?

Widal test is an agglutination test that detects antibodies in a blood sample against two antigens (O & H) of Salmonella bacteria. Agglutination refers to the visible clumping of particles when a particulate antigen combines with its antibody in the presence of optimum conditions for antigen-antibody reaction.
Widal test should only be performed after the first week, as an antibody against “O” and “H” antigens of Salmonella start appearing in the serum at the end of the first week of fever. It is preferable to test two blood samples at an interval of 7 to 10 days to demonstrate rising antibody titres.

How is the Widal Test done?
A blood sample is taken from the vein of your arm. The test can be done by the following two methods
-Slide agglutination method
-Tube agglutination method

When the Widal test is performed in a test tube, it is called Tube agglutination and when it is carried out on a slide, it is called Slide agglutination. Widal test by Tube agglutination is recommended over the latter. The antigens used in the test are “H” and “O” antigens of S. typhi and “H” antigen of S. paratyphi.

What Do the Results of Widal Test mean?
Active typhoid infection is confirmed if the test shows the following:
-Titre of 1:80 or more for O agglutination
-1:160 or more for H agglutination
A rise in titres (4-fold or more) in the two blood samples taken 10 days apart confirms the diagnosis.

When Can the Test be False?

In the early stages of the infection, the test may give a false negative result. False-positive result may be seen due to past infections or vaccination

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