Widal Test is a serological test used in diagnosing typhoid fever, which is bacterial infection caused by Salmonella typhi and occasionally Salmonella paratyphi. Widal Test is often used in developing countries like Pakistan as it is inexpensive and easily accessible. The test detects particular antibodies in a patient's serum against antigens of Salmonella bacteria. The test is normally advised after a week of unrelenting high fever during which the body begins to produce measurable amounts of antibodies.
The Widal test may be carried out by employing two main methods: the widal test slide method that provides immediate but qualitative results and the widal test tube method that provides quantitative titers. Adequate interpretation of the results is essential because false positives can be set up following previous infections or vaccination.
What is a Widal Test?
The Widal test, named after the French clinician Georges-Fernand Widal, is a serological test for enteric fever, i.e., typhoid and paratyphoid fever. Its full name is the Widal agglutination reaction. It is founded on the detection of the presence of antibodies in the patient's serum elicited following infection by widal test for salmonella. The antigens tested are two: 'O' (somatic) and 'H' (flagellar) antigens. High titers of these antibodies indicate active infection.
Widal test uses are where there are no advanced laboratory facilities like blood culture in the setting. However, the validity of the test depends upon the background level of antibody in the population concerned, and this can be very unreliable. It should never be used as the sole sign of diagnosis but together with clinical signs and symptoms.
Why is the Widal Test Done?
Widal test is performed if the symptoms caused by typhoid fever are developed in a patient. The symptoms are typically chronic fever for longer than three to five days, drowsiness, chills, headache, abdominal pain, and constipation or diarrhea in some instances. Doctors order the test when symptoms develop and fever due to malaria or dengue is ruled out.
Where widespread, typhoid must be diagnosed early and accurately in order to start effective antibiotic therapy and avoid such complications as intestinal perforation or chronic disease. The test most becomes predictive within the seventh and tenth day of illness since the immune system requires time to produce detectable levels of antibodies.
How to Prepare for a Widal Test?
Preparation for a Widal test is generally simple. Fasting helps not at all, and patients can eat and drink as usual before the test. But they must inform their doctor if they have recently been immunized with typhoid or are on antibiotics since these might affect the widal test accuracy.
The patients have to provide their entire medical history, such as travel abroad to areas with a typhoid endemic in the past few weeks or contact with an infected person. Wearing a shirt with sleeves that can roll up quite easily on the day of the test is simple because the test itself is to take blood from an arm vein. The test itself is not a long time being uncomfortable and is generally only slightly so.
Widal Test Procedure
Widal test for typhoid is conducted by either the tube method or the slide method in which the serum of the patient is combined with specific antigens of Salmonella bacteria.
Widal test procedure is: With a slide test, a patient's serum of one drop is placed on a glass slide and combined with a drop of antigen solution. If clumping occurs, then the test is positive. The test is rapid and convenient for screening but less reliable than the tube test.
Tube technique is quantitative and more accurate. The patient's serum is serially diluted and added to antigen solutions in test tubes. The mixture is incubated for 2 hours. The tubes are read for agglutination after incubation and the highest dilution where there is still clumping is noted as the antibody titer. The test requires 1 and 2 hours and results are normally obtained on the same day.
Read More: Liver Function Test (LFT): What it is?
What to Do After the Widal Test?
Unless there are complications, there is no specific post-test care required after the Widal test. Patients can return to normal activities immediately after the Widal test. The blood test may cause some bruising, swelling, or soreness at the puncture site, but these will settle within a short time.
When the result comes, the physician will interpret it against the background of history, clinical presentation, and titer values within the region. A positive test should not worry an individual, as the result may not always reflect a current infection.
Understanding Widal Test Results
Widal test report are in titres, for example, 1:40, 1:80, 1:160, etc., and they represent the degree of dilution up to which the antibodies can still be detected. O antigen titre is more typically suggestive of recent or active infection, whereas H antigen titre suggests previous infection or immunization.
In general, widal test normal range are as follows:
- antigen: < 1:80
- H antigen: < 1:160
A widal test positive result generally means:
- titer ≥ 1:160
- H titer ≥ 1:160
Widal test interpretation will depend more on the history of exposure and on locally accepted normal standard. Low titers may be clinically significant enough in an endemic population. A rising titer in widal test sample type taken 7–10 days apart is a stronger indicator of infection.
Diseases Diagnosed by Widal Test
Widal test is most selectively employed for the diagnosis of typhoid fever and paratyphoid fever, both due to two different serotypes of Salmonella. It does not detect other viral or bacterial infections. Although valuable, the test is not always accurate, particularly where people might have been exposed to Salmonella but did not develop disease or have been immunized. This results in false positives. Thus, Widal test is most commonly employed along with the symptoms and, where available, blood cultures for confirmatory purpose.
Widal Test Vs Typhidot
Widal test vs typhidot are two different tests. The Typhidot test is another one of the diagnostic tests used to detect typhoid fever. While the Widal test is one that identifies antibodies by agglutination, Typhidot identifies IgM and IgG anti-Salmonella antibodies using dot ELISA. Typhidot can thus diagnose earlier in the disease course, usually 2–3 days from the first day of fever, whereas the Widal test is more helpful after seven days of illness.
Typhidot is sensitive and specific but generally more expensive. They are generally applied simultaneously in the majority of healthcare facilities for the complete diagnosis. Although still preferred due to its cost and ease of use, Widal can be replaced best by Typhidot, offering faster and perhaps more accurate results at the initial stage of infection.
Widal Test Cost in Pakistan
Widal test price in Pakistan is quite inexpensive, and it can be afforded by anyone. It varies from PKR 400 to PKR 1,000 based on the city and diagnostic centre. It is easily available at government hospitals, private clinics, and diagnostic centres. It can be availed with discounts or even free of cost in a few areas from public health programs, especially in outbreaks. Although cheap, the test is always to be interpreted by a seasoned physician so that it cannot cause misdiagnosis.
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