Widal Test – What Patients Should Know
- Dr. Karuturi Subrahmanyam
- Apr 30
- 2 min read
Updated: 1 day ago
What is the Widal Test?
The Widal test is a blood test used to help diagnose typhoid fever, an infection caused by the bacteria Salmonella typhi. It works by detecting specific antibodies in the patient’s blood that are produced in response to the infection.
Why is the Widal Test Done?
Your doctor may suggest a Widal test if you have symptoms such as:
High and continuous fever
Weakness or fatigue
Headache
Loss of appetite
Stomach pain
Constipation or diarrhea
Recent travel to a place where typhoid is common
How is the Widal Test Done?
A small sample of blood is taken and tested in a laboratory to check for antibodies against Salmonella typhi and Salmonella paratyphi. These antibodies are measured as titers, which show how diluted the blood can be while still detecting the antibodies.
How to Interpret a Widal Test
The Widal test mainly looks for two types of antibodies:
O antibodies – These are produced against the body (somatic) part of the bacteria and usually indicate a current or recent infection.
H antibodies – These are produced against the flagella (tail) of the bacteria and usually indicate a past infection or previous vaccination.
In general:
If the O antibody titer is 1:160 or higher, it may suggest an active typhoid infection.
If the H antibody titer is 1:160 or higher, it may indicate a past infection or vaccination.
If antibodies against Salmonella paratyphi (A or B) are found in similar levels (around 1:80 to 1:160), it may suggest a paratyphoid infection.
However, these values can vary depending on the local background level of exposure to typhoid in your area.
It is also important to remember that:
A single Widal test is not always conclusive. Doctors may ask for a repeat test after a few days to check if the antibody levels are rising.
False positives can occur if you’ve had a past infection or typhoid vaccine.
False negatives can occur if the test is done too early in the illness or if you have already started antibiotics.
So, always trust your doctor to interpret the results along with your symptoms and other test findings.
Limitations of the Widal Test
It is less reliable in the early days of fever.
It cannot always distinguish between past and present infection.
It should not be the only test used for diagnosis—blood cultures are more accurate when available.
Precautions Before the Test
You don’t need to fast before the test. However, inform your doctor if you recently received a typhoid vaccine or have taken antibiotics, as these can affect the results.
Summary
The Widal test is a helpful tool for detecting typhoid fever, but it is not perfect. Results must be interpreted carefully by your doctor. If you have fever and suspect typhoid, consult your doctor promptly. With proper diagnosis and treatment, typhoid can be effectively managed.
Dr. Karuturi Subrahmanyam, MD, FRCP (London), FACP (USA)
Internal Medicine Specialist
Kify Hospital
Danavaipeta
Rajahmundry
Phone : 85000 23456
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