Widal Test, Serum

The Widal agglutination test is used for diagnosing Enteric Fever. The term enteric fever includes typhoid fever caused by Salmonella typhi, Salmonella paratyphi A, B and C. Though enteric fever is endemic in all parts of India, S.paratyphi C infections are uncommon and are not included in Widal testing.

Other names: Typhoid test 

Often, people search for the full form of Widal. The fact is, Georges Ferdinand Widal developed the test, and so the name of the test is called the Widal test after him. A Widal test is used to investigate the presence of H and O serum agglutinins in the patient’s serum.

If you are having symptoms of high fever, fatigue, diarrhoea, constipation, abdominal pain, rashes known as rose spots, dry cough, and headache, there is a probability of typhoid fever. Doctors suggest Widal test in the diagnosis of typhoid fever. 

Why Widal test?

Widal test procedure involves the serum agglutination test to detect typhoid fever. Patients who are suffering from enteric fever will carry homologous antibodies in the serum. The slide method and the tube method are the two types of Widal test procedures. If the serum reacts with the respective antigen, agglutination will happen. Widal test for typhoid is a rapid test diagnostic method, and results are ready on the same day.

The Widal agglutination test is used for diagnosing Enteric Fever. The term enteric fever includes typhoid fever caused by Salmonella typhi, Salmonella paratyphi A, B and C. Though enteric fever is endemic in all parts of India, S. paratyphi C infections are uncommon and are not included in Widal testing.

Who should get the Widal test?

If you are having symptoms of high fever, fatigue, diarrhoea, constipation, abdominal pain, rashes known as rose spots, dry cough, and headache, there is a probability of typhoid fever. Doctor will order this test to diagnose or rule out typhoid.

Reference values for Widal Test :

If the Widal test result is more than or equal to 1:80 titer for antigen O and antigen H, then it indicates typhoid infection.

Interpretation for Widal Test

• Diagnostic titre of Widal test varies highly between different geographical locations. It depends upon the baseline titre prevalent amongst the healthy individuals in that geographical area, which in turn is influenced by endemicity of typhoid in that region.
• The titre of the Widal test will depend on the stage of the disease. Antibodies usually appear by the beginning of second week of infection. Hence, blood taken earlier may give a negative result. The titre increases steadily till the 3rd or 4th week after which it declines gradually.
• Cases treated early with antibiotics may show a poor antibody response.
• A single Widal test is of little clinical relevance due to the number of cross reacting infections, including malaria, tuberculosis, pneumonia, amoebiasis, rickettsia disease, rheumatoid arthritis, hepatitis B.
• A fourfold increase in the titer in paired sera in the course of the infection would be consistent with a typhoid infection.
• Persons who have suffered from enteric fever in the past may show agglutinins in moderate titre, even when suffering from other unrelated illness. Such anamnestic appearance may be differentiated by repeat testing after 7-10 days. Anamnestic response will show only a transient rise, while in enteric fever the rise will be sustained
• TAB vaccinated patients may show a moderate rise in the titers against all three ‘H’, ‘AH’ & ‘BH’ antigens