All Tests
Infection Test

Widal Test

The Widal test is used to investigate typhoid fever (caused by Salmonella Typhi). Understanding what the titre numbers mean, and their limitations, is critical to reading your result correctly.1

Written by Suman Konda, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last reviewed and updated: · How we check our content

Quick answer

The Widal test reports typhoid antibodies as titres: a TO titre of 1:160 or higher suggests active typhoid, and a fourfold rise between samples taken 5 to 7 days apart strongly confirms it. But single results are often unreliable: background exposure, cross-reactions, and prior antibiotics can all mislead. The test only turns positive from day 6 to 10 of illness.

What is the Widal test?

Advertisement

The Widal test measures antibodies against Salmonella Typhi (typhoid) and Salmonella Paratyphi (paratyphoid) bacteria in your blood. It detects four antibodies: TO (Typhi O, body antigen), TH (Typhi H, flagellar antigen), AO (Paratyphi A O), and AH (Paratyphi A H). Results are expressed as "titres", a dilution ratio showing how concentrated the antibodies are in your blood. The higher the titre, the more antibody is present.

Widal Test: How to read titres

AntigenSignificant Titre (single test)What it suggests
TO (Typhi O)≥ 1:160Active typhoid infection
TH (Typhi H)≥ 1:160Past infection or vaccination
AO (Paratyphi A O)≥ 1:160Active paratyphoid A infection
AH (Paratyphi A H)≥ 1:160Past paratyphoid or vaccination
Key points
  • Results are titres (dilution ratios); TO at 1:160 or higher suggests active typhoid on a single test.
  • A fourfold rise between samples taken 5-7 days apart strongly confirms typhoid.
  • Significant cutoffs vary by region (1:80 to 1:320): ask what the lab uses.
  • The test turns positive only from day 6 to 10; a negative first-week result means little.
  • False positives are common in endemic areas from background exposure; malaria and dengue can cross-react.

Note: Significant titre cutoff varies between regions. Some labs use 1:80 or 1:320. Always ask your doctor what cutoff their lab uses.

What does a positive Widal mean?

POSITIVE Titre ≥ 1:160 for TO

A raised TO titre on a single test suggests active typhoid infection, especially with fever, headache, stomach pain and constipation or diarrhoea. However, a single Widal can be misleading. A rising titre, comparing two samples taken 5–7 days apart, is far more meaningful than a single reading. A 4-fold rise in titre (e.g., from 1:40 to 1:160) strongly confirms typhoid.

The big problem with Widal tests

Why Widal results are often unreliable

The Widal test has significant limitations, particularly in typhoid-endemic regions: (1) High false positive rate, many people in endemic areas have background Widal titres from past exposure or previous typhoid vaccination. A titre of 1:80–1:160 can represent normal background levels in endemic populations. (2) Cross-reactions with other infections (malaria, dengue, liver disease) can raise titres. (3) A negative Widal in the first week of typhoid is common, the test becomes positive only from day 6–10. (4) Antibiotic treatment before testing suppresses antibody response.2 The newer rapid tests marketed as replacements are better but not decisive: a Cochrane review of 37 studies in 5,080 patients found average sensitivity of 78% and specificity of 87% for TUBEX, and 84% and 79% for Typhidot. In a group of 1,000 febrile patients of whom 300 truly have enteric fever, that still leaves roughly 66 cases missed and well over a hundred people wrongly labelled.2 For these reasons, blood culture (gold standard) is the most reliable typhoid test, though it takes 3–5 days for results.

Questions to ask your doctor

  • Should we do a blood culture to confirm typhoid rather than relying on Widal alone?
  • What is the background Widal titre in this region?
  • Should we repeat the test in 5 days to look for a rising titre?
  • Do I need antibiotics now or should we wait for culture results?

Pharmacist's practical notes

The single-titre trap drives massive antibiotic overuse: a lone 1:160 in a febrile patient becomes “typhoid” and a prescription, when background exposure explains it perfectly well. Paired sera or blood culture are the evidence-based paths; the single Widal is the shortcut that misleads.

Prior typhoid vaccination raises titres — another reason the number needs the history. And when antibiotics are started, the choice and duration are medical decisions guided by local resistance patterns, not by the titre height; higher titres don't mean stronger antibiotics.

In India

The Widal is reported as titres (1:80, 1:160 and so on) and typically costs &rupee;200–&rupee;400, varying by city. Cutoffs differ between labs because background exposure differs by region — commonly a TO titre of 1:160 or higher is taken as significant.

Where possible, choose a NABL-accredited lab. Blood culture remains the confirmatory test where available — it also guides antibiotic choice.

References

Sources cited on this page. PubMed links open the original abstract.

  1. Olopoenia LA, King AL. Widal agglutination test, 100 years later: still plagued by controversy. Postgrad Med J. 2000;76(892):80–84. PMID 10644383 · doi:10.1136/pmj.76.892.80
  2. Wijedoru L, Mallett S, Parry CM. Rapid diagnostic tests for typhoid and paratyphoid (enteric) fever. Cochrane Database Syst Rev. 2017;5(5):CD008892. PMID 28545155 · doi:10.1002/14651858.CD008892.pub2
  3. Parry CM, Hien TT, Dougan G, White NJ, Farrar JJ. Typhoid fever. N Engl J Med. 2002;347(22):1770–1782. PMID 12456854 · doi:10.1056/NEJMra020201

Why the Widal test has significant limitations

The Widal test, developed in 1896, detects agglutinating antibodies against Salmonella Typhi (O and H antigens) and S. Paratyphi A. Despite its longevity, it is considered unreliable by modern infectious disease standards and is no longer recommended by WHO as the primary diagnostic test for enteric fever in well-resourced settings.

The core problem is low specificity:

  • Antibody titres are affected by prior vaccination with typhoid vaccine (raises baseline titres), prior exposure to non-typhoid Salmonella strains (cross-reacting antibodies), and prior typhoid infection (persistent elevated titres for months after recovery, making reinfection difficult to diagnose).
  • Titre thresholds vary by region and local baseline. A titre of 1:160 for anti-O may be considered significant in a non-endemic area but meaningless in a hyper-endemic area where baseline titres are universally elevated. There is no universal threshold.
  • Antibody production takes 7–14 days from illness onset, the Widal test may be negative in the first week of typhoid fever, precisely when treatment decisions matter most.

Better alternatives to the Widal test

  • Blood culture: The gold standard for diagnosing typhoid fever. Salmonella Typhi is isolated from blood in 40–80% of cases in the first week, with sensitivity highest in the first 2–3 days of fever onset. Bone marrow culture is more sensitive (up to 90%) but impractical.3 Blood culture takes 48–72 hours for a result.
  • Typhoid IgM/IgG rapid tests (Typhidot, TUBEX): These detect IgM antibodies against specific S. Typhi O9 antigen (TUBEX) or outer membrane proteins (Typhidot-M). Sensitivity and specificity are better than the Widal test. A Cochrane meta-analysis found TUBEX averages around 78% sensitivity and 87% specificity, and Typhidot around 84% sensitivity and 79% specificity, across studies in endemic areas.2 Rapid tests provide results within 2 hours, valuable where culture facilities are limited.
  • Widal in resource-limited settings: Where blood culture is unavailable, the Widal test may still be used alongside clinical scoring. NICE and WHO both emphasise that a positive Widal must never be used as the sole basis for typhoid treatment, the diagnosis should be supported by compatible clinical features (fever for more than 5 days, relative bradycardia, rose spots, constipation or diarrhoea, splenomegaly).

Antibiotic resistance in typhoid, a critical concern

Fluoroquinolone resistance in S. Typhi (including extensively drug-resistant XDR typhoid, first detected in Pakistan in 2016) has made empirical treatment difficult. Azithromycin remains active in non-XDR typhoid; XDR typhoid requires third-generation cephalosporins (ceftriaxone) or carbapenems. Culture and sensitivity testing is therefore essential for all confirmed cases, not just for diagnosis but for selecting effective therapy.

Widal myths vs facts

The Widal test is among the most ordered — and most misleading — tests in endemic regions. Here is what the evidence actually says:

MYTH A positive Widal means you have typhoid.

Fact: Not necessarily — in endemic regions, background antibodies from past exposure produce positive titres in healthy people. A single positive Widal is one of the most over-read results in medicine; blood culture is the confirmatory test.

MYTH The higher the titre, the worse the typhoid.

Fact: Titres don't grade severity — they reflect antibody levels, which vary with past exposure and vaccination. A 1:320 isn't ‘worse typhoid’ than 1:160; it's just a higher antibody reading.

MYTH A negative Widal rules out typhoid.

Fact: It doesn't — early in the illness antibodies haven't risen yet, and some patients never mount a strong response. Timing from fever onset decides what a negative means; culture decides the diagnosis.

MYTH Widal is the best test for typhoid.

Fact: Blood culture is — it grows the actual organism and guides antibiotics. Widal is a fallback where culture isn't available, used with paired sera (rising titres) rather than single samples.

Your Widal result: what to do next

Got your report and wondering what the titres mean? Find the branch that matches your situation — every path ends with your doctor:

If your result is…Sensible next stepTalk to your doctor when…
TO titre 1:160 or higherCommonly taken as significant — but interpreted with fever pattern and background exposure.promptly; typhoid treatment decisions need the clinical picture.
Low single titre (e.g. 1:80)Often background exposure in endemic areas — not diagnostic alone.if fever persists; a repeat or culture clarifies.
Rising titres (paired sera)The meaningful pattern — a fourfold rise supports recent infection.for proper interpretation; this is the test used as intended.
Negative with typical feverDoesn't exclude typhoid early on — blood culture is the confirmatory step.promptly; don't let a negative delay evaluation of prolonged fever.

Widal test price in India

In India, the Widal is reported as titres (1:80, 1:160 and so on) and typically costs &rupee;200–&rupee;400, varying by city. Cutoffs differ between labs because background exposure differs by region — commonly a TO titre of 1:160 or higher is taken as significant, but your lab's own cutoff governs. Where possible, choose a NABL-accredited lab, and remember a single titre is never the whole diagnosis.

Frequently Asked Questions

What is the Widal test?
The Widal test measures antibodies against Salmonella Typhi (typhoid) and Salmonella Paratyphi (paratyphoid) bacteria in your blood. It detects four antibodies: TO (Typhi O, body antigen), TH (Typhi H, flagellar antigen), AO (Paratyphi A O), and AH (Paratyphi A H). Results are expressed as "titres", a dilution ratio showing how concentrated the antibodies are in your blood. The higher the titre, the more antibody is present.
What is widal Test: How to read titres?
Note: Significant titre cutoff varies between regions. Some labs use 1:80 or 1:320. Always ask your doctor what cutoff their lab uses.
What does a positive Widal mean?
A raised TO titre on a single test suggests active typhoid infection, especially with fever, headache, stomach pain and constipation or diarrhoea. However, a single Widal can be misleading. A rising titre, comparing two samples taken 5–7 days apart, is far more meaningful than a single reading. A 4-fold rise in titre (e.g., from 1:40 to 1:160) strongly confirms typhoid.
What is the big problem with Widal tests?
The Widal test has significant limitations, particularly in typhoid-endemic regions: (1) High false positive rate, many people in endemic areas have background Widal titres from past exposure or previous typhoid vaccination. A titre of 1:80–1:160 can represent normal background levels in endemic populations. (2) Cross-reactions with other infections (malaria, dengue, liver disease) can raise titres. (3) A negative Widal in the first week of typhoid is common, the test becomes positive only from day 6–10. (4) Antibiotic treatment before testing suppresses antibody response. For these reasons, blood culture (gold standard) is the most reliable typhoid test, though it takes 3–5 days for results.
Why the Widal test has significant limitations?
The Widal test, developed in 1896, detects agglutinating antibodies against Salmonella Typhi (O and H antigens) and S. Paratyphi A. Despite its longevity, it is considered unreliable by modern infectious disease standards and is no longer recommended by WHO as the primary diagnostic test for enteric fever in well-resourced settings.
How much does the Widal test cost in India?
There is no single fixed price — it varies by city, lab, and whether the test is ordered alone or as part of a panel. NABL-accredited labs usually publish their rates online, so it is worth comparing a couple near you. Whatever you pay, the reference range printed on your own report is what counts — discuss the result with your doctor.
What Widal titre is considered positive in India?
Commonly a TO titre of 1:160 or higher is taken as significant, but there is no universal cutoff — labs set their own based on local background exposure. Go by your lab's reference and your doctor's judgement, not a number from the internet.
Can the typhoid vaccine affect my Widal result?
Yes — vaccination can raise typhoid antibodies and produce a misleading positive. Always mention any typhoid vaccination when the test is ordered so the result is interpreted correctly.
If my blood culture is positive, do I still need a Widal?
No. A positive blood culture is definitive — it has found the bacteria itself. The Widal adds nothing once culture has confirmed typhoid.
Why is the Widal still used if it is so unreliable?
Because it is cheap, fast and available where blood culture is not. In many settings it is the only feasible test — used carefully, with paired samples and clinical context, it still has a role.
Medical Disclaimer: This page is for general educational purposes only and does not constitute medical advice. Always consult a qualified doctor before making any health decisions.
Written and medically reviewed by Suman Konda, Clinical Pharmacist · Sources linked to PubMed · Not medical advice: see our disclaimer