Infection Test

Widal Test

Name: Widal Test: Normal Range & What Positive Means
Creator: Suman Konda
Published: 2026-07-05

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.

Written and clinically reviewed by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last reviewed and updated: 01 August 2026 · How we check our content

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.

Widal Test: How to read titres

Antigen	Significant Titre (single test)	What it suggests
TO (Typhi O)	≥ 1:160	Active typhoid infection
TH (Typhi H)	≥ 1:160	Past infection or vaccination
AO (Paratyphi A O)	≥ 1:160	Active paratyphoid A infection
AH (Paratyphi A H)	≥ 1:160	Past paratyphoid or vaccination

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. 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?