What is WidalTest? Know everything about WidalTest here

The agglutination test that detects serum agglutinins and its presence in patients with paratyphoid or typhoid fever is termed as WidalTest. This test is a milestone achievement in the field of medicine. If the facility for culturing isn’t available, the test proves a reliable way to diagnose typhoid fever. The test was developed in the year 1896 by Georges Ferdinand Widal whereby the serum of the patient is tested for H antibodies and O antibodies or agglutinins. The test is performed at two intervals and between 7-10 days. With the passage of 7-10 days, titer antibody rises in the serum and thus the test must be performed twice. The doctor can also prescribe you psa test or prostate specific antigen test which measures the amount of PSA in the bloodstream of a male.

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What is the principal of the test?

The test relies on the fact that if any homologous antibody is present in the serum of the patient, it would certainly react with reagent’s antigen and thus shows visible clumping in the test report or card. Here the antigens used in the particular test are ‘O’ and ‘H’ antigens. ‘O’ antigen is for Salmonella Typhi whereas ‘H’ is for SParatyphi.

Why is the test performed?

The test is considered as the most reliable test for enteric fever by the bacteria which causes malaria or typhoid. In this Serological test, the serum is blended with the antibody of the person or patient. The test is performed to diagnose typhoid. It is popular test for typhoid used since a century. It gives confirmed report whether or not the patient is suffering from Typhoid. It measures agglutinating antibody level in the serum against H and O antigens. If carried out on the 10th day of the disease, the report will be positive. But, if the patient received TAB vaccine, the report will still be Positive, but falsely positive.

When to opt for the test?

The reliable test is popular for detecting enteric fever. If the Typhoid fever is acute, O Agglutinins will be detected some 6-8 days following the onset of Typhoid fever while the H Agglutinins can be detected within 12 days of the onset of Typhoid fever. So, it is important to test two different specimens of the serum.

The ways to reading the report

It is quite easy to read the report. You need to look for highest dilution of serum. After finding the highest dilution, check for any agglutination. As per the reports, if the test ends with 1:320, it is titer. If the report reads positive, then it is Typhoid. When the ‘O’ antigen titer is more than 1:160, it is known as active infection infamously. But, if ‘H’ antigen is higher or greater than 1:160, it suggests past infection in immunized person. The agglutination test is helpful for varied diagnosis or differential diagnosis.

Whether you are prescribed tsh test or Widal, it is important to ensure that the report is correct. When there is problem in Thyroid gland, the doctor prescribes thyroid stimulating hormone test.


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