Widal test

What it measures

Detects agglutinating antibodies against Salmonella Typhi and Paratyphi O and H antigens. It is widely used but has major limitations and should not be relied on alone.

Specimen and preparation

• Specimen: Serum
• Tube: Red top
• Preparation: Paired samples 7–10 days apart are more meaningful than one.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Enteric fever (fourfold rise in O titre in paired sera)
• Past typhoid or TAB vaccination (mainly H)
• Cross-reacting infections: malaria, dengue, other salmonellae

Method

Slide or tube agglutination

Good to know

Limitations: low sensitivity in week 1, false positives from endemic exposure, vaccination and cross-reaction; antibiotics blunt the response. Blood culture is the diagnostic standard.

Related tests