Widal Test
The Widal test detects antibodies against O and H antigens of Salmonella typhi and paratyphi. It has been used for typhoid diagnosis for over a century but is now controversial because false positives are common in typhoid-endemic areas (previous infection or vaccination raises baseline titres) and false negatives occur early in illness. Blood culture remains the gold standard; the Widal is supportive evidence at best and should be interpreted with caution.
Expected Result
Normal
Non-significant titre (varies by endemicity)
In endemic India: O ≥1:160 and H ≥1:320 suggest current infection, but paired samples are more reliable than single titres.
This is a qualitative test — results are reported as positive or negative rather than as a numeric range. Interpretation may vary by laboratory method; always review with your doctor.
What a Negative Result Means
A non-significant Widal titre early in illness does not rule out typhoid — antibodies may not have risen yet. Repeat in 7–10 days. If typhoid remains likely (persistent fever, rose spots, relative bradycardia, eosinopenia), blood culture is the definitive test. Modern alternatives include typhoid PCR and IgM rapid tests which are more specific than Widal.
What a Positive Result Means
A significantly elevated Widal — especially a four-fold rise on paired samples 7–10 days apart — supports typhoid fever in someone with compatible symptoms. Single high titres are less reliable in endemic areas because baseline titres may already be high. False positives occur in brucellosis, malaria, rickettsial infection, and after typhoid vaccination. Always interpret with clinical features and, ideally, blood culture.
Frequently Asked Questions
Why is the Widal test controversial?
In typhoid-endemic areas, residual antibodies from past infection or vaccination keep baseline titres high — so 'high' titres are common in healthy people. The test also has poor sensitivity in the first week when antibiotics may be critical. WHO, ICMR, and most Indian guidelines recommend blood culture as the primary test and use Widal only as adjunctive evidence.
What is a significant Widal titre in India?
In endemic India, O agglutinin titre ≥1:160 and H agglutinin titre ≥1:320 are often considered significant. Paired samples showing a four-fold rise between acute and convalescent phases (7–10 days apart) is more reliable than a single value. Individual labs may set slightly different thresholds based on local baselines.
Should Widal be used to diagnose typhoid?
Widal is no longer preferred. Blood culture (especially in the first week) remains the gold standard — it confirms the organism and allows antibiotic sensitivity testing, which is crucial given rising multi-drug resistance in Salmonella typhi. If fever and clinical suspicion persist, get a blood culture rather than relying on Widal alone.
Related Infectious tests
See all →ASO Titre (Anti-Streptolysin O)
Antibody against streptococcal toxin — evidence of recent strep infection.
IU/mLInfectiousDengue NS1 Antigen
Early dengue virus antigen — detectable in the first week of fever.
InfectiousDengue IgM Antibody
Antibody that rises in the second week of dengue infection.
InfectiousDengue IgG Antibody
Antibody marking past or long-term dengue infection.
This information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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