GRUBER WIDAL TEST
Widal reaction is specific reaction consisting in agglutination of typhoid bacilli when mixed with serum from a patient having typhoid fever or other salmonella infection and constituting a test for the disease. Widal Test is an agglutination test which detects the presence of serum agglutinins (H1 and O2) in patients serum with typhoid and paratyphoid fever. When facilities for culturing are not available, the Widal test is the reliable and can be of value in the diagnosis of typhoid fevers in endemic areas. It was developed by Georges Ferdinand Widal in 1896. The patient’s serum is tested for O and H antibodies (agglutinins) against Salmonella antigens.
Widal Test
The main principle of widal test is that if homologous antibody is present in patients serum, it will react with antigen in the reagent and gives visible agglutination in the tube. The antigens used in the test are H and O antigens of Salmonella Typhi.
The titre of the patient serum using Widal test antigen suspensions is the highest dilution of the serum sample that gives a positive result (Titers are expressed by the denominator only, for example 1:256 is written 256). The sample which shows the titre of 100 or more for O agglutinations and 200 or more for H agglutination should be considered as clinically significant (active infection).
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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