Typhoid fever is caused by Salmonella typhi and related organisms.

The Widal test detects O (somatic) and H (flagellar) antibodies against Salmonella antigens.

The tube method is more accurate than the slide method, as it provides quantitative titers of antibodies.

Clinical uses include:

Confirming typhoid and paratyphoid fever.

Monitoring antibody levels in suspected cases.

Supporting diagnosis in patients with fever, abdominal pain, and gastrointestinal symptoms.

Limitations:

Cross‑reactivity may cause false positives (malaria, dengue, other infections).

Baseline titers vary by region, so interpretation must consider local endemic values.

Rising titers in paired sera (taken 7–10 days apart) are more diagnostic than a single test.

Analyte: Antibodies against Salmonella typhi (O & H antigens) and Salmonella paratyphi (A & B antigens).

Normal Result: Negative or insignificant titers.

Abnormal Findings:

Significant titers (≥1:160 or rising titers): Suggest typhoid or paratyphoid infection.

O antibody: Indicates acute infection.

H antibody: Indicates past infection or immunization.

Clinical Use:

Provides a quantitative measure of antibody levels.

Helps guide diagnosis, monitoring, and treatment decisions.

Supports infectious disease and general medicine evaluations.