Widal Test (Tube Agglutination)

Also known as Typhoid Test (Tube Agglutination)

You need to provide

Blood

This test is for

Male, Female

Test Preparation

No special preparation required

Understanding Widal Test (Tube Agglutination)

What is Widal Test (Tube Agglutination)?

The widal test (Tube agglutination) is a blood test that detects enteric fever – Typhoid and Paratyphoid fever. Enteric fever is a systemic infection caused by bacteria, usually through ingestion of contaminated food or water. The symptoms of typhoid fever include high fever, diarrhea, headache, constipation, and stomach pain.
Widal test detects antibodies (agglutinins) in a blood sample against two antigens (O & H) of bacteria Salmonella enterica. In some cases where culturing facilities are not available, this test is reliable and can add value in the diagnosis of typhoid fever. Typhoid fever can be treated with antibiotics, while vaccination is also useful in the prevention of the disease.

What is Widal Test (Tube Agglutination) used for?

The Widal test is performed:

To diagnose Enteric fever (Typhoid and Paratyphoid fever)

Interpreting Widal Test (Tube Agglutination) results

Interpretations

If the antibody against Salmonella is present in patient’s serum, it will react with the respective antigen in the reagent and give visible agglutination (clumping) at the bottom of the test tube after 18 hrs.

The highest dilution of the patient’s serum sample that gives a visible agglutination with the Widal test antigen suspensions is the antibody titre.

The serum sample which shows the titre of 1:80 or more for O agglutination and 1:160 or more for H agglutination indicates active infection. A rise in titres (4-fold or more) in the two blood samples taken 10 days apart confirms the diagnosis. Please note that different labs may have different reference values for the interpretation of the Widal test.

The interpretation of a Widal test is greatly influenced by the nature and extent of the patient’s previous contact with typhoid antigens. It can be either due to clinical or subclinical infection with typhoid or related organisms or from typhoid vaccination. The lesser the extent of the previous contact, the greater is the usefulness of the Widal test.

Answers to Patient Concerns & Frequently Asked Questions (FAQs) about Widal Test (Tube Agglutination)

Frequently Asked Questions about Widal Test (Tube Agglutination)

Q. Is there any preparation required before the test?

Inform the doctor about the medications you may be taking. No other specific preparations are usually required before this test.

Q. What are the different methods for performing Widal test?

Widal test can be performed by the following two different methods: 1. Slide agglutination Widal test Qualitative Slide Test Quantitative Slide Test 2. Tube agglutination Widal test Tube agglutination is the recommended method as it has more accuracy. However, Slide agglutination is preferred by some as it gives the rapid result. Tube agglutination method requires approximately 18 hours for test completion.

Q. Is there any risk associated with this test?

There is no risk associated with the test. However, since this test involves a needle prick to withdraw the blood sample, in very rare cases, a patient may experience increased bleeding, hematoma formation (blood collection under the skin), bruising or infection at the site of needle prick.

Q. What are the limitations of Widal test?

The limitations of Widal test are: Previous typhoid vaccination may result in increased antibody titres in the non-infected persons False positive Widal test can occur in patients with non-enteric Salmonella infection, for example Typhus, Immunological disorders, chronic liver disease, Malaria and cryptococcal meningitis Prior use of antibiotics can affect antibody response giving a low titre in the Widal test even in the presence of bacteriologically confirmed typhoid fever The Widal agglutination titre varies with the geographic location based on the prevalence of Salmonella infection in that area Past infection with serotype Typhi or another nontyphoidal Salmonella serotype also results in false positive Widal test

Q. What are the other tests to diagnose Enteric fever?

The other tests which are used to diagnose Enteric fever include Blood culture test, Widal test, Stool culture test, and Urine culture test. Among these, blood culture is the most commonly recommended method for diagnosing Enteric fever and is performed during the first week of fever. If in case other test results come inconclusive then bone marrow samples can be used to diagnose any infections.

Q. How can you prevent typhoid fever?

Avoiding contaminated foods and drinks can help to prevent typhoid fever. Along with that, proper vaccination against typhoid fever can also keep a check on developing any possible case of infection.

Q. What is the appropriate time during illness for performing Widal test?

Widal test should be performed after first week of fever. The reason being,the antibodies against “O” and “H” antigens of Salmonella, start appearing in the blood of patients by the end of 1st week, with sharp rise in 2nd and 3rd week and the antibody titre remains steady till 4th week after which it starts declining. It is preferable to test two blood samples at an interval of 7 to 10 days to demonstrate a rising antibody titres.

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