10/08/2025
Widal Test
1. Objective:
The objective of the Widal test was to detect antibodies (agglutinins) against the Salmonella typhi and Salmonella paratyphi antigens in a patient’s serum, helping diagnose enteric (typhoid) fever.
2. Principle:
The test was based on agglutination reaction between specific Salmonella antigens and corresponding antibodies in the patient’s serum. If antibodies were present, they reacted with the antigens to form visible clumps.
3. Materials:
Patient's serum (collected in a plain tube)
Widal antigen suspensions:
S. typhi O (somatic) antigen
S. typhi H (flagellar) antigen
S. paratyphi A and B H antigens
Glass slide or test tubes
Pipettes and mixing sticks
Physiological saline
Water bath/incubator (if tube method)
Timer and light source
4. Procedure:
Slide Method (Rapid):
1. A drop of patient serum was placed on a glass slide.
2. Equal drops of each Widal antigen were added.
3. The mixture was rotated gently for 1 minute.
4. Agglutination was observed visually.
Tube Method (Quantitative):
1. Serum was serially diluted in test tubes.
2. Equal volumes of antigen suspension were added.
3. Tubes were incubated at 37°C for 16–20 hours.
4. Agglutination was read visually and the antibody titer was recorded.
5. Result:
Positive: Agglutination observed; a titer of ≥1:80 or fourfold rise in paired samples was considered significant.
Negative: No visible agglutination.
6. Uses:
It was used to aid in the diagnosis of typhoid and paratyphoid fever.
Helped monitor disease progression or response to treatment.
7. Consultation:
Positive results prompted referral to a physician or infectious disease specialist. Antibiotic therapy was started based on clinical correlation, and blood culture was advised for confirmation.
