test Details

Typhoid disease, paratyphoid disease, enteric fever

Typhoid is a disease common in developing countries caused by the bacteria Salmonella typhi. Typhoid fever and paratyphoid fever (also known as enteric fever) are diseases caused by the consumption of contaminated food or water.

The Widal test can be performed by two methods, namely, tube agglutination and slide agglutination. The tube method has been found to be more accurate. The test principally tests the titre of antibodies produced in the body against S. typhi A, S. typhi B and S. paratyphi A, S. paratyphi B and paratyphi C. These are all the subtypes of bacteria responsible for causing typhoid and paratyphoid disease.

The Widal test might be advised by your doctor in case you have a gastrointestinal infection. The symptoms include fever, weakness, body aches, vomiting, loose stools, headache, skin rashes and loss of appetite. If you have some of these symptoms, your doctor might suspect typhoid and advise a Widal test for confirmation. 

Typhoid has an incubation period of about one to two weeks. This means that the symptoms begin to appear after that much time following the exposure to infection.

The symptoms of paratyphoid infection are also similar but milder. The disease also generally has a shorter incubation period and recovery is faster as well.

Repeat testing is not necessary as it is only recommended by medical professionals when the symptoms of enteric fever disease show up in the patient. The final diagnosis is made with a combination of clinical examination, patient history and blood test. A stool examination or urine examination may be recommended. In severe cases, a bone marrow test may be required.

However, during the course of your infection, the Widal test may be repeated. This is to look for a rising titre that indicates a gradually increasing production of antibodies and is an essential component of active infection. This helps to confirm the diagnosis.

Other names of the Widal test

• Typhoid blood test
• Enteric fever test
• Paratyphoid test

What does the Widal test detect or measure and who is this prescribed for?

The Widal test measures the titre of antibodies in the blood. In case of any response in the body, the immune system produces antibodies to fight the infection. The titre of these antibodies can indicate the severity of the infection.

The test report provides information on individual antibody titres. A positive response to S. typhi O is indicative of currently active typhoid infection. A positive response to the S typhi H antigen indicates that you had the infection at some point in the past. Both these antigens are present at different locations in the bacteria.

The following symptoms prompt the consulting physician to prescribe you a Widal test along with other blood tests:

• Fever - this may start as a low-grade fever, but the temperature gradually rises every day and temperatures often exceed 104℉ degrees Fahrenheit
• Joint pain and muscle pain
• Fatigue
• Headache (often very severe)
• Abdominal pain
• Diarrhoea
• Nausea and vomiting
• Loss of appetite
• Skin rash

The interpretation of the Widal test varies in different areas as typhoid is endemic in certain places. Laboratories provide a baseline value of the particular area and the test is interpreted accordingly.

The results are considered in context with the existing symptoms and the baseline of the area.

In areas such as India, where typhoid infections are common, the results have to be interpreted accordingly. In these endemic areas, due to repeated exposures and cross-infections, false positives are common.

Patients may be found to have low titres of positive antibodies even in the absence of active infection. If no further tests (such as urine or stool examination or cultures to grow bacteria) can be performed, the Widal test can be used as follows:

• The test is repeated and a fourfold increase in the titer is checked for during the course of the same episode of infection. This means the presence of antibodies even in a fourfold dilute solution (e.g., from 1:40 to 1:640) in the course of the infection.

• The type of antibodies is checked to look for a conversion from an IgM reaction to an IgG reaction. This change should be of at least the same titer. IgM antibodies are usually seen in the initial active phase of the infection. As this settles, it converts to the more chronic IgG antibody.

The results of a Widal test are based on a blood sample. A blood sample is drawn from a prominent vein of the arm. No special preparation is required.

Test Preparation

Before the test

There are no special preparations required before taking a Widal test. However, the concerned physician can be consulted regarding precautions to be taken before depending on the patient's medical history and physical factors.

During the test

The procedure for blood sample collection for a Widal test is similar to other general blood tests. A blood sample is drawn from a prominent vein of the arm. No special preparation is required.

 This process barely takes 5 minutes.

After the test

Like any other blood test, after sample collection, the point of contact is cleaned and pressure is applied on the spot to stop any bleeding. There is little to no risk from this test and there are no post-test restrictions either.

Test inclusion: What parameters are included?

The Widal test is a tube agglutination test. It primarily measures the antibody response in the body in case of the presence of typhoid antigen. The test consists of separating the serum of the patient from the blood sample.

It uses a series of tubes that contain a suspension of the bacteria Salmonella. The antigens detected include Salmonella typhi O and H, Salmonella paratyphi O, AH and BH. A test report will give the antibody titre in response to each of these antigens. Any positive response is indicated by clumping.

How frequently should you take this test?

A Widal test is not a test that needs to be done at regular intervals. Your doctor may advise it due to the presence of symptoms such as fever, headache, body aches, fatigue and abdominal symptoms.

The results of the Widal test indicate whether or not these symptoms are due to infection by the bacteria Salmonella which causes typhoid fever and paratyphoid fever. This test might be recommended along with several other tests to diagnose the cause of your symptoms.