When Should You Opt For Widal Test? How To Prepare For It?

When Should You Opt For Widal Test? How To Prepare For It?

The Widal test is an agglutination test that helps to detect the presence of serum agglutinins in the patient’s serum that has fever and typhoid. If you have no time for culture, you can try out the Widal test which is very reliable and can indeed of great value for diagnosing the kind of typhoid fever in the endemic areas. This test has been developed by Georges Ferdinand Widal in 1896 and thus the name.

The serum of the patient is tested for O and H antibodies against various antigen suspensions. You can know more about your disease kind with the help of the Widal test report. The Widal test is a straightforward and inexpensive test that takes just a few minutes, and it helps to detect the presence of salmonella antibodies in a patient’s serum.

Why Would You Use The Widal Test?

The Widal test is known to be one of the most reliable serological tests for enteric fever or undulant fever by bacteria causing typhoid and malaria where the serum is mixed with a specific antibody, which is obtained from an individual. This test is a mostly used diagnostic test for typhoid fever in all developing countries. Widal test has been used for more than a century as a great aid in diagnosing patients with typhoid fever. This test helps in measuring the agglutinating antibody levels against O and H antigens. If you perform the analysis on the tenth day after the disease, then the test results will be positive and may be falsely positive if an individual previously received a TAB vaccine

When To Go For the Widal Test?

According to the various doctors across the world, the Widal test is considered as a highly reliable test that helps in diagnosis of enteric fever, which is also better known as typhoid. The Widal test was developed by Georges Ferdinand Widal in 1896. The Salmonella antibody starts appearing in serum at the end of the first week and rises sharply during the 3rd week of endemic fever.

During 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 thus important to test for at least two specimens of sera at an equal interval of 7 to 10 days to exhibit a rising antibody titre.You can use the Salmonella antigen suspensions as the slide and the tube techniques.

How To Prepare For The Widal Test?

There are myriad genres in which you can make for a Widal test. This test can be conducted in two kinds of ways

  • Slide agglutination Widal test
    1. In the Qualitative Slide Test way
    2. In the Quantitative Slide Test way
  • Tube agglutination Widal test
  • The second kind of tests gives you more accurate results compared to the slide widal test. A slide widal test is, however, more popular among diagnostic laboratories as it provides rapid and immediate results.

So How are this Two Kind of Widal Tests Performed [Procedure]

The Qualitative Slide Test

  • You need to bring all the reagents to a temperature that matches the room and mix them well
  • Then add a drop of the test sample into each of the reaction circle. The different spheres label as O, H, AH, BH as per the given antigen solution.
  • Then Add a drop of positive control into the circle which marks as PC and one fall of negative control into the reaction circle that has marked as NC
  • You would need to add the antigen solution of the Salmonella typhi ‘O,’ Salmonella typhi ‘H,’ Salmonella paratyphi ‘AH’ and Salmonella paratyphi ‘BH’ to circles labeled as O, H, AH, BH respectively
  • Mix the mixtures well with an applicator stick and then rotate the slide gently and then see if you can see any agglutination.

The Quantitative Slide Test

  • You would first need to bring the substances at perfect room temperature and mix it thoroughly well.
  • Dole out one drop of saline into the first reaction circle and then place different values ul of the test sample in the remaining circles.
  • You would then need to add a drop of the antigen, which showed agglutination with the test sample in the screening method, to each circle.
  • Take the help of an applicator and Mix the contents of each circle well and rotate the slide gently.
  • Observe for agglutination.

The Quantitative Tube Test

  • You would first need to bring the substances at perfect room temperature and mix it thoroughly well.
  • Prepare four sets of test tubes for pouring in individual antigen
  • Add 1.9 ml of 0.85% sterile saline to tube no. 1 of each antigen set
  • Add 1 ml of physiological saline to all the other tube sets
  • You would need to transfer 1 ml of the diluted serum sample from tube No. 1 to tube No. 2 and mix well
  • Continue this procedure one by one in all test tubes
  • Discard 1.0 ml of the diluted serum from tube No.7 of each set.
  • Tube no. 8 is known be under negative control with 0.85% sterile saline.
  • Add Salmonella paratyphi ‘AH’ and Salmonella paratyphi ‘BH’ to all the tubes from 1-8.
  • You would need to Mix the solution well, cover and incubate these tubes all through the night at 37 degrees Celsius
  • After incubation removes the sediment and scrutinizes thoroughly for agglutination.

How to Read Widal Test Report [Interpretation]

  • The process of reading this report is quite comfortable where you will have to check for the highest dilution of the serum, and once you have found the highest dilution, then you will have to check for agglutination.
  • According to the various reports in case if it ends at 1:320 then that is the titer
  • For most of the cases but then, if in case, you see the Widal test is positive.
  • Please note, if “O” antigen titer is greater than 1:160, which is infamously called active infection. Also, we have seen, if “H” antigen titer is higher than 1:160, that mainly indicates the past infection or in immunized persons.

These are the various ways in which you can read the Widal test report.

Medically Reviewed By
Dr. Kaushal M. Bhavsar (MBBS, MD)Assistant Professor in Pulmonary Medicine, GMERS Medical College, Ahmedabad