Widal test (Slide method)

Strong immunity is key to living a happy life. The immune system protects our body from external sources which can harm our body, such as bacteria, etc. However, when an individual happens to consume contaminated food, it can have varying adverse effects on the body, including ingestion of bacteria like Typhoid and Paratyphoid.

An individual can also get infected by Typhoid by using a toilet that was contaminated with bacteria and touching body parts without washing hands, contaminated milk products, unhygienic street food and carrier cases those asymptomatic. Typhoid fever or Typhoid is caused by Salmonella typhi bacteria.

Typhoid occurs 8 to 48 hours after the bacterial infection and remains 2 to five days. A patient with Typhoid carries the bacteria in their bloodstream and intestinal tract. It's an acute, life-threatening and fever-causing illness. Typhoid fever is often confirmed through blood testing. Widal test (or Typhidot test) is a rapid serological test for the diagnosis of Typhoid.

The Widal test is performed through the slide method. When the typhoid bacilli are mixed with the blood sample containing typhoid antibodies from a patient with Typhoid, agglutination occurs. This means the presence of typhoid bacteria.

Physicians may recommend the Widal test when they suspect Typhoid. This test can quickly diagnose if a patient is affected by enteric or Typhoid fever. If a patient has the symptoms of fever with chill, fatigue, headache, abdominal pain, constipation, weight loss and rash spots, the doctor may recommend a Widal test to the person.

Widal test requires blood sample, which is collected by phlebotomists by venipuncture of the arm.

Test Preparation

Before the test

If you're on any medications, inform the doctor. No other specific preparations are required before the Widal test.

During the test

The procedure for sampling blood for a Widal test is analogous to other general blood tests. A Phlebotomist collects the blood from the vein of the arm under all aseptic precautions. This process barely takes 5 minutes.

After the test

After the sample is taken, the purpose of contact is cleaned and pressure is applied on the spot to prevent any bleeding. There's little to no risk from this test and there are not any post-test restrictions.

Test inclusion: What parameters are included?

Widal test is done to detect antibodies within the blood sample against antigens O & H of bacteria. Agglutination is the clumping of a particular antigen with its antibody in the presence of appropriate conditions. Slide agglutination and tube agglutination are two ways of administering this test.

A Widal test should be performed after the first week of infection. The reason for this is that the antibodies against “O” and “H” antigens start appearing in the blood at the peak of the first week of fever. It is advised to get two blood tests at an interval of 7 to 10 days.

Typhoid and Paratyphoid fever

Widal test helps detect Typhoid or paratyphoid infection.

Without correct diagnosis and treatment, you may be at risk of complications, such as-    

•  Inflammation of heart muscle or pancreas
•  Intestinal perforation
•  Kidney or bladder infections
•  Pneumonia
•  Infection and inflammation of the membranes
•  Psychiatric problems, such as restlessness, hallucinations and more.

The normal values and reference ranges of the test may vary from lab to lab. Please refer to the ranges mentioned in the report and consult a doctor to understand the interpretation of lab reports.

If the antibody against the bacteria is present within the patient’s serum, it'll react with the respective antigen within the reagent and provide visible agglutination (clumping) on the test slide. The highest dilution of the patient’s blood sample that provides a clear agglutination with the Widal test antigen suspensions is that of the antibody titre.

If the Widal test is positive, it indicates that the person has the Salmonella enterica serovar Typhi infection. During a positive report, which indicates the presence of the Typhoid infection and test reflects the presence of both O and H antigen titres. S typhi O positive means active infection of typhoid. Active infection is a sign of an infection of Salmonella enterica serovar typhi. S typhi H positive shows the results of the immunised person’s serum test report or means there's a past infection

A titre of 1:80 or more for O agglutination and 1:160 or more for H agglutination in the blood sample indicates active infection. If the blood samples taken after a duration of 10 days from the original sample show a rise in titres (4-fold or more), it confirms the diagnosis.

Widal test negative means that a person does not have enteric/typhoid fever and there is another infection causing the symptoms. If the titre value of antigen O and H is below 1:160 in the sample, the result is a negative Widal report. The interpretation of the Widal test depends upon the lab conducting the test, as most labs have different values for interpretation.

The results of a Widal test are heavily influenced by the extent of the patient’s last known contact with typhoid antigens. The lesser the extent of the previous contact, the greater is the accuracy of the Widal test.