Widal test (typhoid O and H agglutinins)

The overall reading of a Widal test, which looks for antibodies to typhoid bacteria. It is easy to misread and cannot confirm typhoid on its own.

AI-verified against cited sources. Awaiting expert reviewAlso called Widal

What it is

The Widal test is a blood test used in some countries to look for typhoid fever. It mixes your blood serum with killed typhoid bacteria and looks for clumping, using the bacterium's outer surface (O) and its whip-like tail (H). Labs report a titer for each, such as 1:80, and often add a one-line reading such as negative, not significant or positive. This marker holds that overall reading. The separate O and H titers have their own pages.

Why it matters

A Widal result is often used to decide whether a fever might be typhoid, but it is one of the least reliable tests for the job. The CDC calls it unreliable and prefers blood culture to confirm typhoid, and WHO guidance also stresses confirming it with a culture. A positive reading does not prove typhoid, and a negative reading does not rule it out. Your clinician weighs the reading with your symptoms, travel, vaccines and other tests.

If it’s high

A positive or significant reading means your O or H titer reached the lab's cutoff. It can be a sign of a current or recent typhoid infection. It can also reflect an old infection, a typhoid vaccine, living where typhoid is common, or a cross-reaction with another infection. In one audit of 100 febrile children in New Delhi, only 5 of the 54 children with a positive Widal had typhoid confirmed by blood culture.

Common causes

Past exposure to Salmonella bacteria, which is common where typhoid is widespread
A typhoid vaccine, because antibody tests cannot tell vaccination from infection
Another infection that cross-reacts with the test
A current typhoid or paratyphoid infection (enteric fever)

What can help

Talk with your clinician about what the reading means alongside your symptoms, travel and vaccine history
Ask whether a blood culture would be more reliable for you
Ask whether a second sample later in the illness would help, since a rising titer says more than one result

What can affect your result

How long you have been sick: antibodies take time to rise, so an early sample can be negative
Where you live or have lived: baseline titers are higher in areas where typhoid is common
Typhoid vaccination and past infection
The lab's method and kit: slide and tube versions differ, and each lab sets its own cutoff for a significant titer
Typhoid vaccination and past typhoid infection can raise titers, and antibody tests cannot tell them apart from a current infection (CDC Yellow Book).
Healthy people who live in, or come from, an area where typhoid is common often have a raised baseline titer. In a study of healthy adults in Jammu, India, 45.7% reacted to Typhi O and 21.2% to Typhi H.
Some people whose fever had another proven cause, such as malaria or dengue, still had raised titers in a large Vietnam study, so a raised result can be a false positive.
The slide version often has no firm threshold for a positive, and any visible clumping can be read as positive (WHO Bulletin 2026). The tube version is more informative when two samples are compared, but cutoffs still differ between labs.
A sample taken early in the illness can be negative because antibodies take time to rise.

Antibodies take time to rise, so an early sample can be negative. A second sample taken later can show whether the titer is rising (WHO Bulletin 2026).

When to talk to a clinician

See a clinician soon about a high fever that lasts more than a few days, especially with headache, belly pain, constipation or diarrhea, or a rash, or if the fever started after travel to an area where typhoid is common. Typhoid can be treated but can cause serious complications. Get urgent care if you feel very weak, are confused, have severe belly pain or cannot keep fluids down.

Questions you could ask

Is the Widal test the right test for my situation?
If this reading is negative but I still have a fever, what are the next steps?
Could my symptoms, travel or vaccines explain this reading?
Would a blood culture or another typhoid test be more reliable for me?
Should we repeat the test later to see whether the titer is rising?

Questions people ask

Is the Widal test accurate?

Not very. A review of 20 studies found it picked up about 63% of cases and correctly cleared about 73% of people without typhoid, on average. Health agencies prefer blood culture to confirm typhoid.

What do 'not significant' and 'significant' mean on my report?

They show whether your titer reached the lab's own cutoff. Labs choose different cutoffs, and there is no standard one, so the same titer can be called significant at one lab and not at another.

Why might my doctor repeat the test?

A single result cannot show whether antibody is rising. When a second sample later in the illness is compared with the first, a rise says more than either result alone.

Show the science and sources

For clinicians and researchers

The Widal test detects agglutinating antibody to S. Typhi O and H antigens (with Paratyphi AH and BH on extended panels) and can be run as a slide or tube test. It lacks validated cutoffs for acute disease and has variable sensitivity and specificity in endemic settings, because pre-existing antibody, cross-reactivity and the inability to separate acute from past infection reduce its value (WHO Bulletin 2026). The slide version often has no threshold, so any visible reaction may be called positive. The tube version is more informative when paired samples show a rise. A 2025 review of 20 studies reported mean sensitivity of about 63% and specificity of about 73%. In Vietnam, a cutoff of O 200 or H 100 detected 74% of 1,400 culture-proven cases, and at 30.8% prevalence 14% of positive results were false and 10% of negative results were false. Blood culture sensitivity is roughly 50 to 65% (about 50% for a single culture per CDC). The CDC calls the test unreliable and prefers blood culture; a WHO Bulletin commentary says WHO guidance emphasizes microbiological confirmation and that CDC recommends against Widal serology, and India's National Essential Diagnostics List does not include the test.

Sources

Typhoid and Paratyphoid Fever (CDC Yellow Book), Centers for Disease Control and Prevention
Typhoid (fact sheet), World Health Organization
A case for eliminating Widal testing for enteric fever, India, Bulletin of the World Health Organization (2026)
Value of a single-tube Widal test in diagnosis of typhoid fever in Vietnam, Journal of Clinical Microbiology (1999)
Estimation of Baseline Widal Antibody Titers among Apparently Healthy Urban Population of District Jammu, Indian Journal of Community Medicine (2021)
Evaluating alternatives to the Widal test for typhoid fever diagnosis in developing countries: A targeted literature review, Journal of Public Health in Africa (2025)
Role of modified Widal test in the diagnosis of enteric fever, Journal of the Association of Physicians of India (2003)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.