Are you dealing with a persistent fever that does not go away? Do you have stomach issues or a general feeling of being unwell? Chances are high that your doctor will suggest a Widal test. 

But do you know what a Widal test is? Why is the Widal test important? Most of us are unaware and may get anxious when a doctor suggests such a test. This guide is an attempt to identify what makes the Widal test an important asset for doctors. 

What is Widal Test? 

A Widal test is a type of blood test that lets doctors determine if you have Typhoid. It can also be used to diagnose Paratyphoid fever. The test can be compared to a detective searching for clues in your bloodstream to find if you are infected with Salmonella bacteria that cause typhoid.

When the bacteria enter your body due to contaminated food, your immune system develops antibodies to fight this infection. The Widal test looks for these antibodies in your bloodstream. Presence of these antibodies confirms that you have an infection. 

The test is named after Georges-Fernand Widal, a French physician who developed this diagnostic method. The test belongs to the category of agglutination tests, where the antibodies club together when mixed with certain antigens from the Salmonella bacteria. 

Importance of Widal Test

Why is Widal test important? What is Widal test used for? Well, we already know the answer. However, going a bit deep into it can help us understand the test and its results a bit better. 

Typhoid fever has been considered to be one of the dangerous enteric fevers. As per WHO, it affects around 10 to 20 million people globally each year and causes approximately 126,000 to 161,000 deaths annually. That is exactly why an accurate diagnosis becomes extremely necessary. 

Widal test is a very common method to test typhoid. 

The test also lets the doctors find how you are responding to the treatment. It is used to confirm that you are no longer carrying the bacteria. 

Preparations for the Widal Test

The best thing is that Widal test does not require any sort of preparation. There is no need to fast before the test. 

However, it is essential to take care of a few things before the test so that the results will be accurate. 

• Timing of the test - The test should be taken at least one week after the fever begins. Early tests may not give accurate results.
• Recent vaccinations – Let the doctor know about any recent vaccinations that you might have had. These can affect the test results.
• Antibiotic use – If you have taken any antibiotics in recent times, let the doctor know about them. These, too, affect the results of a Widal test. 

It is also important to share the details about your recent travel history, contact with anyone who has typhoid, and details of any contaminated food that you might have had. These factors will determine if you really have typhoid and, if yes, what is the extent of infection. 

Benefits of Widal Test

Widal test has been considered the first test in fighting typhoid and similar enteric fevers. It offers multiple advantages that make it the right choice to opt for. 

• Quick and simple – The test is quite quick and simple. It involves a little blood sample and analysing it. The test in itself is quite non-invasive and does not need any preparation. It can be performed in most of the laboratories without the need for specialised equipment.
• Cost-effective- Widal test is highly cost-effective and can suit a wider population. In many developing countries, it has been treated to be highly affordable.
• Access to past and current infection – The test also provides valuable information on both past and present infections. It can help you detect different types of antibodies, doctors can distinguish between an active infection and one that occurred in the past.
• Suitable for every age group – Widal test is an excellent option for all age groups. Since it is minimally invasive, there are no significant side effects associated with the test. 

Procedure used in the Widal test 

The Widal test procedure is easy and simple. As we have already witnessed, it does not need you to prepare specifically for it. However, understanding how a Widal test is performed helps you avoid the unnecessary anxiety related to the test.

The procedure begins with the doctor collecting a little blood sample from your veins. The blood is generally drawn from a vein near your elbow. Once collected, the blood sample is sent to the laboratory where the actual test takes place. The test follows two major methods - the slide method and the tube method.

The slide method

It is used typically for initial screening. The technician will drop the blood on the slide. Then they will add different types of Salmonella antigens to separate sections of the slide. These antigens will include O antigen (from the bacterial cell wall), H antigen (from the bacterial flagella), and sometimes AH and BH antigens for paratyphoid detection.

The technician mixes the serum with three antigens and then rotates the slide. If there are any antibodies in the bloodstream, they will react with the antigens and cause a clumping. This process is called agglutination. 

If the initial screening is positive, a more precise test is performed. This will involve testing different dilutions of your blood serum to determine the exact titre or concentration of antibodies present.

The Tube method 

The Tube method is considered to be more accurate and is used specifically for confirming the results. In this method, multiple tubes are used with different dilutions of the serum. 

Antigens are added to each tube, and the mixture is incubated overnight at body temperature. The tube showing agglutination indicates the titre of the antibodies present in the bloodstream. 

The complete process takes around 24 to 48 hours. 

The Normal Range for Widal Test Results 

It is important to understand the Widal test normal range. Let us explore the normal range of results so you have a clear understanding of what each of these values means. 

The Widal test results are expressed as titres, which represent the dilution at which agglutination occurs. The normal range for the Widal test is typically a titre of 1:80 or below for both O and H antigens.

• S. Typhi O antigen – A titre of 1:160 or higher generally indicates an active typhoid infection. If you find your O antigen is elevated, it is a clear indicator that you have an ongoing infection.
• S. Typhi H antigen – A titre of 1:160 or higher may indicate either a current infection or a past infection. The H antibodies develop more slowly than O antibodies but persist longer in your bloodstream.
• S. Paratyphi antigens (AH and BH) – The similar ranges will be applicable. A titre of 1:80 or below is considered normal, while 1:160 or higher suggests paratyphoid fever.

Here is a simple breakdown of what you can expect –

For O Antigen:

• 1:20 to 1:80: Normal range, no active infection
• 1:160 or higher: Positive result, suggests active typhoid infection

For H Antigen:

• 1:20 to 1:80: Normal range
• 1:160 to 1:320: Borderline, may indicate recent or past infection
• Above 1:320: Positive result, suggests current or recent infection

It should be worth noting that the ratings and readings will range slightly based on the laboratory you have chosen and the geographical region that you belong to. 

The baseline antibody levels can be different for different populations. 

Interpretation of Widal Test Results 

Interpreting the Widal test results cannot be that straightforward. That is why it is essential to have an expert doctor by your side when interpreting these results. 

Positive test results 

It should always be remembered that a positive result may not necessarily mean you have typhoid fever. A negative result may not necessarily mean you do not have the infection. 

The positive results indicate that the antibodies against Salmonella Typhi or Paratyphi have been found in your bloodstream. If you have O antigen titre is 1:160 or higher, it means you have an active infection. An elevated H antigen level indicates an ongoing or past infection. 

It is quite possible to get a false-positive result on a Widal test. If you have had a past infection or have a had vaccination, the results may be positive. You may also get positive results if you have certain other medical conditions. 

Negative test results

A negative Widal test result means that you have no antibodies present in your bloodstream. It will clearly suggest that you have no active infection of typhoid fever. However, the timing of the test should be important here. 

If you take the test too early in the face of the infection, you may get a negative result. That would mean you will be declared negative even when you have an active infection going on. 

Your doctor may recommend a repeat test after 7 to 10 days of the initial negative result. This is done specifically when the doctor suspects a typhoid infection despite a negative result. 

Ideally, the test results would be interpreted based on the specific patterns –

• Only O antigen is elevated – It indicates an early or acute infection.
• Both O and H antigens are elevated – The infection is present for a long time
• Only H antigen is elevated – It indicates a past infection or a vaccination. It generally is not an indicator of an active case. 

Factors that Influence the Widal Test Results 

There are several factors that affect the accuracy of the Widal test results. That is exactly why doctors recommend this test as a broader diagnostic picture. However, they may not rely on it alone. 

Previous vaccination 

Any prior vaccination can yield a false-positive result. If you have received a typhoid vaccination recently, your body will have antibodies developed against the bacteria. You will have a positive test result even when you are not infected. 

Prior typhoid infection 

A prior infection can also affect the accuracy of the result. The elevated levels of antibody may persist even months after the infection has subsided. That would make it difficult to distinguish between the active infection and the lingering antibodies in the body. 

Use of antibiotics 

The use of antibiotics can affect the results in the opposite way. It can cause false negatives. If you have begun taking the antibiotics before the Widal test, the bacteria may get suppressed partially. It can lead to lower-than-expected antibody levels. 

Timing of the test 

If you are testing too early in the infection, antibodies might not have developed yet. That would result in a false negative. It is recommended to take up the tests at least after one week after your symptoms begin. 

Other infections and medical conditions 

Some medical conditions can cause false positives. These health conditions can include malaria (especially falciparum malaria), dengue fever, certain liver diseases, rheumatoid arthritis, and kidney disorders.

A few other conditions that can affect the Widal test results can include sample quality and lab techniques used, geographical variations, and cross reactivity. 

Wrapping Up

Widal test is one of the most important tests for diagnosing typhoid and other enteric fevers. Of course, it has its own limitations, but still, the tests form an important step in treating typhoid and other concerns effectively. 

Ready to take the next step? If you suspect you might have typhoid fever or have been exposed to someone with the infection, schedule an appointment with your healthcare provider today. Amrita Hospitals, being one of the leading healthcare provider in Kochi should be your one-stop solution to assess your symptoms, order appropriate tests, including the Widal test if needed, and guide you through the treatment process. Your health is too important to delay. Get tested, get treated, and get back to feeling your best.

FAQs

What is the Widal Test used for?

Widal test is used for diagnosing typhoid fever and paratyphoid fever. It helps detect the antibodies belonging to the Salmonella Typhi or Salmonella Paratyphi bacteria. 

When Do You Need a Widal Test?

You should get Widal test if you have symptoms of typhoid fever. The symptoms include persistent high fever (often increasing gradually over several days), severe headache, abdominal pain, loss of appetite, weakness and fatigue, and rashes. 

What does Widal test positive mean?

Elevated Widal test results indicate that you probably have typhoid or paratyphoid fever. An elevated H antigen titre suggests either a current or a past infection. If your O antigen titre is 1:160 or higher, it indicates an active infection.

How long does it take to get the Widal test reports?

Most of the laboratories provide you the Widal test results in 24 to 48 hours. The timing would be dependent on the type of test – whether slide test or tube test. 

Does a Widal test require fasting?

No. The Widal test does not require any fasting. You can eat and drink as usual. There are no special dietary restrictions or preparation requirements for this test.