Widal tube

The Widal test for diagnosis of typhoid and paratyphoid fevers is one among the simplest and inexpensive laboratory techniques to set up. The Widal test, which was devised by George Widal in 1896, determines the level of antibodies which are specific to Salmonella Typhi and Salmonella Paratyphi and are present in the patient's blood. 

Principle of the Widal test is agglutination reaction, antibodies memorialized in the patient’s blood will agglutinate with the antisera containing specific antibodies to the Salmonella Typhi and Salmonella Paratyphi. Blood serum from the patient is diluted and put into several test tubes containing Salmonella Typhi and Salmonella Paratyphi antigens. The tubes are incubated for a few hours to allow for reactions to occur. 

The Widal test evaluates the concentration of antibodies to Salmonella Typhi and Salmonella Paratyphi in blood. This test determines the concentration of two types of antibodies in the blood: 

• H antibodies (IgG)– these antibodies are formed in response to flagellar antigen of Salmonella Typhi & Salmonella Paratyphi. 
• O antibodies (IgM) – these antibodies are formed in response to somatic antigens of Salmonella Typhi & Salmonella Paratyph. 

The Widal test is normally conducted: 

• For a fever, headache, abdominal pain, and other symptoms of typhoid and paratyphoid fever, or, 
• Following a recent travel to a region where typhoid or paratyphoid fever is frequent, or, 
• After potential contact with a patient with typhoid or paratyphoid fever. 

The Widal test is regarded as safe and reasonably priced. However, there are some drawbacks: false negatives can occur in the initial stages of the disease or between most tests if the patient has taken antimicrobials. 

• A different infection present in the patient can lead to false-positive results. 
• Immunodeficiency disorders may render this diagnosis ineffective when identifying patients suffering from typhoid fever or paratyphoid fever. 

The Widal test has the following attributes that it assesses: 

• H antibody titer: This depicts the concentration of both IgG antibodies directed against the flagellar antigen of Salmonella Typhi or Salmonella Paratyphi. 
• O antibody titer: This depicts the concentration of both IgM antibodies directed against the somatic antigen of Salmonella Typhi or Salmonella Paratyphi. 
• Blood serum dilution: The patient's blood serum is diluted in different ratios to ascertain the concentration where agglutination can be seen through the highest dilution. 

Widal test is most useful for: 

• Patients who demonstrate signs of infection of typhoid fever or paratyphoid forms. 
• Patients who have returned from areas prone to typhoid fever or paratyphoid forms of infection. 
• Patients who were in contact with a person suffering from typhoid fever or paratyphoid fever. 

The Widal test is of great help in the diagnosis of typhoid fever and paratyphoid fever which can highly aid int the speedy recovery from the diseases alongside other potential treatment appropriate to the individual. This test is both easy to take and inexpensive. 

Typhoid fever: Infection caused by a bacterial organism Salmonella Typhi. 

Paratyphoid fever: Infection caused by a bacterial organism Salmonella Paratyphi. 

1. Those undergoing the test do not have to do anything different. 
2. A blood sample will be drawn from a tributary vein of the elbow. 

Prerequisites: Your attending physician will explain the requirements to you prior to the test. 

Eligibility: The test can safely be performed by everyone, but usually, it is expected of people having signs and symptoms of the fever associated with Salmonella typhi and Salmonella paratyphi. 

Procedure for Taking the Test: 

• Blood sample will be drawn from a tributary vein of the elbow. 
• The blood sample is analyzed in a laboratory. 

Caution Before the Test: Notify the physician managing your care before the test is done, in case you used an antibiotic or received a vaccine.