Overview

A fever that refuses to settle after four or five days is a common reason to visit an OPD in India, and typhoid is usually high on the list of suspects. The Widal test is one of the blood tests commonly ordered at that point a quick, affordable way to check whether your body has begun responding to the bacteria that cause typhoid.

It is a supporting test, not a confirming one. The test that actually confirms typhoid is a blood culture, which grows the bacteria themselves and shows which antibiotics will work. If typhoid is suspected, the blood culture sample should be taken before any antibiotic is started, because even one or two doses can make the culture negative.

What is Widal Test?

The Widal test looks for antibodies your body produces against Salmonella Typhi and Salmonella Paratyphi, the bacteria that cause typhoid and paratyphoid fever (collectively called enteric fever).

It checks four antigens: the O antigen (somatic) and H antigen (flagellar) of S. Typhi, plus AH and BH for S. Paratyphi A and B. O antibodies appear around days 6 to 8 and fade quickly, so they suggest active infection. H antibodies appear around days 10 to 12 and can stay in the blood for years after an earlier infection, so a raised H value alone may be an echo of something long past. The typhoid vaccines used in India today contain only the Vi antigen, which this test does not look for so being vaccinated does not make your Widal test positive.

Why Timing Matters in the Widal Test?

The Widal test can be performed perfectly and still come back negative if it is done too soon. Antibodies take time to build. In the first three to five days of fever, most patients have not yet produced enough antibodies to cross the detection threshold, so an early test often reads negative even in someone with typhoid.

The test is most informative from the end of the first week onwards, typically in the second week. Doctors often ask for a repeat sample seven to ten days later, because a fourfold rise in titer between two samples indicates active infection far more reliably than a single reading. Antibiotics started beforehand can also blunt the response.

When is the Widal Test Recommended?

Your doctor is likely to suggest a Widal test when fever has persisted for more than four to five days without an obvious cause, particularly during or just after the monsoon. It is also considered when symptoms fit the pattern of enteric fever. Sustained fever with abdominal discomfort and a change in bowel habit or after eating outside, drinking untreated water, traveling to a typhoid-prone area, or contact with a case at home.

Symptoms to Watch Out for Before Undergoing a Widal Test

Consider speaking to a doctor about testing if you notice:

Fever lasting more than 4–5 days, often rising step-like and peaking in the evening.
Persistent headache and body ache that routine medication does not settle.
Abdominal pain, bloating or tenderness, especially around the navel
Constipation or loose stools, sometimes alternating.
Loss of appetite, nausea and weight loss over a short period
Weakness out of proportion to the fever
A coated tongue, or a faint pink rash (rose spots) on the chest or abdomen

What is the Widal Test Procedure

Blood sample collection: A technician draws a small blood sample from a vein in your arm.
Serum separation: It is centrifuged to separate the serum, which carries the antibodies.
Slide Agglutination Test: In the slide agglutination method, drops of serum are mixed with each antigen on a slide and watched for clumping. This is only a rapid screening step . A result based on the slide method alone is not reliable enough to diagnose typhoid, and should be confirmed by the tube method.
Tube Agglutination Test: In the tube agglutination method, the serum is diluted in stages (1:20, 1:40, 1:80, 1:160, 1:320 and so on) and incubated with the antigens. The highest dilution still showing clumping is reported as the titre.

No fasting is needed. Tell the lab or your doctor about any antibiotics you have taken in the last few days, as these can blunt the antibody response and make the test read negative.

Interpretation of Widal Test Results

Both O and H normal (≤ 1:80): Usually suggests no active typhoid infection, although testing too early in the first week may give a false-negative result.
O and H titres of 1:160 or above: May be suggestive of an active typhoid infection, particularly when both are raised and the result matches the patient's symptoms and illness duration.
Only O titre is raised: May carry more significance because O antibodies are more closely associated with a current or recent immune response. However, the result should not be interpreted on its own.
Only H titre is raised: May reflect past exposure or previous infection and does not necessarily indicate an active typhoid infection.
Higher titre: A higher number, such as 1:320, means antibodies remain detectable even after greater dilution. However, a higher titre does not automatically confirm active infection.
No universal cut-off: Widal test cut-offs vary by region. In India, where typhoid is endemic, low antibody titres may be present in healthy people because of previous exposure. ]
Interpret with other findings: Doctors interpret the Widal result along with symptoms, the day of illness, examination findings and other test results. The tube agglutination method is preferred for reporting titres, while the slide method is mainly used as a rapid screening test.

What are the Limitations of the Widal Test?

The Widal test is supportive rather than confirmatory, and its accuracy varies widely. Reported sensitivity ranges from roughly 47% to 82%. False positives can follow a past typhoid infection you may never have noticed, malaria or dengue, and cross-reaction with related bacteria.

Vaccination is not a cause. The typhoid vaccines used in India do not contain the antigens this test measures. False negatives occur when the test is done too early, after antibiotics have begun, or when the Vi antigen masks the O antigen.

A single sample also cannot separate a current infection from an old one, and it says nothing about which antibiotic will work, which is a real concern given rising drug resistance. This is why blood culture remains the gold standard. It promotes the organism's growth and guides treatment. Doctors often send a culture alongside the Widal test in the first week, when culture is most likely to be positive and the Widal test least likely to be.

Why Should You See a Doctor?

See a general physicians doctor if you have a persistent fever, headache, weakness, abdominal discomfort, loss of appetite, or other symptoms that may suggest an infection, particularly if they continue for several days or worsen. If your Widal test shows a positive or raised titre, consult a doctor for proper interpretation and further evaluation, as the result should be considered along with your symptoms and other tests.

Whether you have been advised to undergo a Widal test, are experiencing persistent fever, headache, abdominal discomfort, weakness, or other symptoms, Narayana Health can help you understand your test results and guide you towards appropriate evaluation and care.

Conclusion

The Widal test is an inexpensive supporting test in the evaluation of a prolonged fever, but its value depends almost entirely on when it is done and how it is read. Tested too early it can miss typhoid; read without clinical context it can suggest typhoid that is not there.

It cannot confirm the diagnosis on its own, and no treatment decision should rest on it alone — a blood culture, ideally collected before antibiotics begin, remains the test that confirms typhoid and guides treatment. If a fever has lasted more than four or five days, do not self-diagnose from a lab report or start antibiotics on your own. It is also worth reading about preventing water-borne infections at home.

Frequently Asked Questions

1. What is the normal range for a Widal test?
There is no single normal range. In endemic regions like India, titres of 1:80 or below are usually background from past exposure. A titre of 1:160 or above in both the O and H antigens, done by the tube method, may suggest active infection but only your doctor can judge that alongside your symptoms.

2. On which day of fever should the Widal test be done?
Ideally after the first week, usually in the second. Testing in the first three to five days often gives a false negative.

3. Can the Widal test be positive without typhoid?
Yes. A past typhoid infection even a mild one you did not notice as well as malaria, dengue and some other bacterial infections can raise titres. Typhoid vaccination does not.

4. Is the Widal test better than a blood culture?
No. Blood culture identifies the bacteria directly and shows which antibiotics will work. The Widal test is quicker and cheaper, so it supports rather than replaces it.

5. Do I need to fast before a Widal test?
No fasting is needed.