How Does Widal Blood Test Procedure Help in Detecting the Typhoid Fever?

Widal Blood Test, or Typhidot, is a fast serological test employed to diagnose typhoid disease. The Typhidot test is a dot ELISA kit that detects IgM and IgG antibodies against the Salmonella typhi outer membrane protein (OMP). The test relies on specific IgM and IgG antibodies against a 50KD OMP. Within 2-3 days of infection, the typhoid test separately detects IgM and IgG antibodies.

The Widal blood test is the most often used typhoid fever diagnostic test in developing countries. The Widal test has been used to aid in diagnosing typhoid disease. It detects the amount of agglutinating antibodies to O and H antigens. The test is positive after the tenth day of the sickness, although it might be false if the person has previously received a typhoid vaccine.

The patient’s blood serum is examined for O and H antibodies to various antigen suspensions. The Widal test report helps to learn more about the disease kind. The Widal test is an easy and inexpensive test that may detect the presence of salmonella antibodies in a patient’s serum in just a few minutes.

The Principal of the Widal Test

The Widal test is based on the antigen-antibody agglutination response principle. A visible clumping is created when a homologous antibody combines with a specific insoluble antigen that promotes its synthesis in the presence of a particular electrolyte at the optimal temperature and pH.

The organisms that cause enteric fever have two primary antigens: a somatic antigen (O), a flagellar antigen (H), and another surface antigen, Vi.

During infection with typhoid or paratyphoid bacilli, antibodies against flagellar antigens of S. Typhi (H), S. paratyphi A (AH), S. paratyphi B (BH), and S. paratyphi Somatic Antigen (O) are commonly detectable in blood six days after infection begins. The Typhidot test only gives the result as positive or negative.

The Uses of the Widal Test

The typhoid screening test is used to diagnose, treat, and monitor the fever and other salmonella diseases. This is done to see if there are any antibodies to the infection. Typhoid or enteric fever is a life-threatening fever, and here are a few symptoms:

  • Low to high fever
  • Headache and body pain
  • Loss of appetite and weight Loss
  • Weakness and Fatigue
  • Dry cough
  • Sweating
  • Abdominal pain
  • Swelling in abdomen
  • Diarrhea or constipation
  • Itching or rashes

Preparation for the Widal Test

The Widal test needs no preparation. It would be best if you informed the doctor about previous vaccinations or health conditions, along with the presence of any other infections. All these factors would be helpful for the correct diagnosis of typhoid fever.

The Procedure of the Widal test

There are two ways to do the Widal test:

1.Widal test for slide agglutination

  • Slide Test (Qualitative)
  • Slide Test (Quantitative)

2. Widal test for tube agglutination

When compared to slide agglutination, tube agglutination is more accurate. A slide widal test, on the other hand, is more common among diagnostic laboratories since it provides quick results.

  • The Widal test is carried out on blood serum. As a result, a blood sample must be taken from the individual.
  • For a better comparison, some laboratories may take samples twice, while others may take a single sample based on the standardization available.
  • A lab worker will wipe the area on your arm with a cotton swab and apply a tourniquet above the designated spot to make a vein apparent before taking the sample.
  • They will draw a small blood sample into a small closed test tube with a sterile needle.
  • The technician will wrap the area with cotton gauze to halt bleeding once enough sample has been obtained.
  • Finally, they’ll apply a bandage to the affected area. 

The Widal Test Results and Normal Values

Interpreting a Widal test is pretty straightforward if you know what you’re looking for. The level of O and H agglutinin titers is an essential factor. It is normal if this number is less than 1:160. If it’s over 1:160, you may develop typhoid fever or another salmonella-related sickness. 

The quantity of reaction (agglutination) between the person’s antibodies and the test solution determines how the test is graded. The following table shows the relationship between test scores and outcomes:

0 means no reaction

1+ means 25% reaction

2+ means 50% reaction

3+ means 75% reaction

4+ means 100% reaction 

when the score is 0, it is considered a normal result. It means that the person is not suffering from typhoid fever.

The test also involves diluting blood serum to look for the presence of a reaction. The technician double-checks the required dilution to ensure there is no response. As a result, the dilution may be stated in the test reports for ease of understanding. However, a negative result does not rule out the possibility of infection because it could be attributable to a person’s poor antibody response. 

Abnormal Results:

A result other than 0 is regarded as abnormal, indicating that the person is suffering from typhoid fever. The doctor may prescribe additional tests to confirm the diagnosis because the test’s sensitivity has been questioned. In most industrialized nations, a blood culture test is recommended to verify the presence of S. Typhi in a sample. The patient’s sample is placed on a specialized medium to encourage bacterial growth, and the culture is then examined under a microscope.

The Final Word

Typhoid fever can be prevented and controlled with safe drinking water, good sanitation, and adequate medical care. Unfortunately, in many underdeveloped countries, achieving these goals may be challenging. As a result, some scientists believe that vaccinations are the most effective strategy to prevent typhoid disease. If you experience any symptoms, it is best to visit your doctor and get them diagnosed. The widal test plays a crucial role in detecting and ensuring one’s health and getting the proper care at the right time.

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