Widal Test Price, Reasons, Procedure, Normal Range, Interpretation

The Widal test is one of the oldest tests devised for the diagnosis of typhoid fever, a bowel disease caused by the bacteria Salmonella typhi.

It checks the presence of anti typhoid antibodies in the patient’s blood. Antibodies are a type of specific protein that our body produces against pathogens.

For the test, a patient’s blood samples are taken at approximately 10 to 14 day intervals (to notice changes in antibody levels in acute and convalescent serum).

After this, put the samples on a slide. Typhi antigen (s. typhi antigen) (protein/part of pathogens against which antibodies are formed).

Two types of S. typhi antigen (S. typhi antigen) are used for the Widal test.

This includes:

• O or somatic antigen: present in the cell wall of S. typhi, the O antigen is less immunogenic (the body produces fewer antibodies against it).
• H or Flagellar Antigen: Present in flagella (tiny threads or hair-like structures that help bacteria to move), H antigen is highly immunogenic.

If the patient’s sample contains antibodies against any of these antigens, agglutination (Visible Clumping) will be seen on the slide.

A fourfold increase in antibodies in the sample (seen more clearly through agglutination) would indicate the presence of S.typhi in the body.

It is important to note that the Widal test does not differentiate between different types of intestinal fever, and gives false-positive results; therefore, it is now used as a confirmatory test in most developed countries. 

Doctors look for other tests and symptoms to confirm the diagnosis of typhoid fever. However, in many developing countries, due to resource constraints, Widal still remains the test of choice for typhoid fever.

The Widal test is mainly used as a diagnostic method for the diagnosis of typhoid fever. This condition spreads through contaminated food and water and appears with the following symptoms:-

• Continuous fever for more than 2 days and body temperature showing between 103 and 104°F
• Stomach pain, loss of appetite
• Diarrhea or constipation
• Weakness and headache
• Cough
• Some people may also have rashes on the skin (skin rash).

If you have any of the above symptoms, your doctor may ask you to do a Widal test to check whether you have S. typhi infection.

The test procedure is done on blood. Hence, there is a need to collect a blood sample from the individual.

Some laboratories may collect samples on two separate occasions for better comparison, while some may collect a single sample depending on the standardization available in their setup.

To take the sample, a lab technician first cleans the area on your arm with a cotton swab, and will tie a tourniquet over the selected area to make a vein prominent. 

Using a sterile needle, they will draw a small amount of blood into a small closed test tube. Once a sufficient sample has been collected, the technician will cover the area with cotton gauze to stop the bleeding. Finally, they will put a bandage over the area.

You may experience slight discomfort due to the prick of the needle, but it subsides soon. Apart from this, some bruises may appear on your skin after the test. But this confort may go away after some time.

If you notice persistent bruising, pain or swelling at the site of sample withdrawal, inform your doctor as soon as possible.

You don’t really need any special preparation for the Widal test. 

Before the test, it is important that you inform your doctor if you have had any previous vaccinations for typhoid fever.

It is also important to tell the doctor about the presence of any other infection, such as malaria, or if you have been in close contact with a person infected with the bacteria that causes typhoid. 

These factors will be helpful in the correct diagnosis of typhoid fever.

Normal result

Test results are scored according to the amount of reaction (agglutination) between the individual’s antibodies and the test solution. The list given below shows the relationship between test score and result:-

When the score is 0, it is considered as a normal result and the person is not suffering from typhoid fever.

In order for the test to react, blood serum is diluted. The technician checks the dilution that needs to be reached so that there is no reaction. Therefore, for simplicity of interpretation, the dilution is also written in the test report.

However, showing a negative result does not rule out, completely, the possibility of infection. Because it may be due to a diluted antibody reaction in a person.

Abnormal Result

A value other than 0 is considered abnormal, and means the person may have typhoid fever.

Since the sensitivity of the test has been repeatedly questioned, the doctor may order further tests to confirm the diagnosis.

Nowadays, a blood culture test is recommended in most developed countries to confirm the presence of S. typhi in the sample.

In this test, the patient’s sample is placed on a special medium to promote bacterial growth and the blood culture is then examined under a microscope.