Widal (Tube Agglutination)
Widal (Tube agglutination)
Widal (Tube agglutination) test is a blood test that is used to identify typhoid and paratyphoid fever, also known as enteric fever. Enteric fever is a bacterial infection that is caused by the faeces of an acutely infected individual, a recovering individual, or a chronic asymptomatic carrier. The incubation period for enteric fever is 6–30 days, which is the period of time between exposure to an infection and the onset of initial symptoms.
The antibodies develop in response to enteric fever. Widal (Tube Agglutination) test detects antibodies (agglutinins) in a blood sample against two Salmonella enterica antigens (O & H).
Enteric fever that results from bacterial infections include
· Typhoid fever which is caused due to Salmonella enterica serotype Typhi (S. Typhi)
· Paratyphoid fever which is caused due to Salmonella enterica serotypes Paratyphi A (S. Paratyphi A), Paratyphi B (S. Paratyphi B), or Paratyphi C (S. Paratyphi C)
Thus, getting this test done is recommended for the diagnosis of enteric fever as early diagnosis and treatment can prevent serious typhoid fever complications like intestinal bleeding or perforation
Symptoms of typhoid fever and paratyphoid fever
Sustained high fever
Headache
Stomach pain
Diarrhea
Constipation
Fatigue
Cough
Test preparation
No special preparation is required for a Widal (Tube Agglutination) test
Interpretation of the Test Results
Positive test result
· If the patient's serum contains an anti-Salmonella antibody, the reagent's corresponding antigen will be activated and cause visible agglutination (clumping) at the bottom of the test tube after 18 hours.
· The antibody titre is the highest dilution of the patient's serum sample that causes an observable agglutination with the Widal (Tube Agglutination) test antigen suspensions.
· Active infection is indicated by serum samples with titres of 1:80 or higher for O agglutination and 1:160 or higher for H agglutination.
· The diagnosis of enteric fever is confirmed by a rise in titres (fourfold or more) in the two blood samples collected ten days apart.
Negative test result
A negative test result shows that there was no agglutination (clumping) at the bottom of the test tube, meaning that there are no clinically significant levels of the corresponding antibody in the patient's serum
FAQs
How is the sample collected for a Widal (Tube Agglutination) test?
A blood sample is taken from a vein in the arm using a fine needle. This procedure typically takes no longer than five minutes
What are the risks involved in a Widal (Tube Agglutination) test sample collection?
This test involves negligible risk. There might be slight pain or tenderness around the site where the needle went in. Rarely, the site can become infected.
What is the turnaround time (TAT) for the result of a Widal (Tube Agglutination) test?
The Widal (Tube Agglutination) test result is usually available within the same day the sample was collected; sometimes it could take longer
When is a Widal (Tube Agglutination) test performed?
If an individual suffers from typhoid or paratyphoid symptoms, such as having a consistent fever for 4 to 6 days, then a Widal (Tube Agglutination) test is recommended by the doctor. This test identifies patients with typhoid and paratyphoid fever who have serum O antigen and H antigen agglutinations
What are the limitations of a Widal (Tube Agglutination) test?
The limitations of Widal (Tube Agglutination) test include:
· Increased antibody titres may be found in people who have previously received typhoid vaccination.
· False positive results from the Widal (Tube Agglutination) test can be caused in individuals who have non-enteric Salmonella infections, such as typhus, immunological disorders, chronic liver disease, malaria, and cryptococcal meningitis.
· Even in the presence of bacteriologically confirmed typhoid fever, prior antibiotic use can affect antibody response, resulting in a low titre in the Widal (Tube Agglutination) test.
The Widal agglutination titre varies by geographic location depending on the prevalence of Salmonella infection in that region.
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