• 05 August, 2025
• By Admin

How To Read Widal Test Report: A Step-by-Step Explanation

The Widal test is one of the most common diagnostic options that doctors employ in case of a suspicion of having typhoid fever. The report can be confusing to many patients with numbers, dilutions and antibody titres. This tutorial will allow you to read a Widal test report and make sense of it step-by-step, and why it would matter to your health.

What Is a Widal Test?

The Widal test is a straightforward blood exam that identifies the antibodies (agglutinins) that your body develops as a reaction to being infected with Salmonella typhi, the bacterial signs of typhoid fever. It is also searching for two specific types of antibodies:

• O antigen (somatic antigen) – Indicates an acute or current infection.
• H antigen (flagellar antigen) – Suggests past infection or vaccination response

Salmonella paratyphi A and B antibodies are sometimes also tested.

How to Read the Report

Your Widal report normally has titres, which are dilutions of a solution that, when you add antibodies, still allow you to see agglutination of the bacteria and the antibodies. These titres are presented in the form of ratios such as 1:20, 1:40, 1:80, 1:160, 1:320, etc. The greater the second figure, the more the sample is diluted.

Here’s how to interpret the results:

• O antigen titre ≥1:160 → Suggests recent infection with Salmonella typhi.
• H antigen titre ≥1:160 → Indicates past infection or ongoing immune response.
• Paratyphi A or B titres ≥1:80 → May indicate paratyphoid infection.

Note: Interpretation depends on the region and the regional prevalence. In endemic countries such as India, lower titres are not infallible.

Step-by-Step Reading Guide

1. Check the O antigen first
   • A raised O antigen is the strongest sign of a current typhoid infection.
2. Look at the H antigen next
   • Helps confirm exposure, but doesn’t always mean active disease.
3. Compare with baseline titres.
   • In India, baseline titres are often 1:20 to 1:40. Anything significantly higher (e.g., 1:160 and above) is more suggestive of typhoid.
4. Rule out false positives
   • Cross-reactivity with malaria, dengue, or past vaccinations may alter the results.
5. Always correlate with symptoms
   • Fever, abdominal pain, headache, and loss of appetite must match the lab findings for diagnosis.

Limitations of the Widal Test

While still widely used, the Widal test has some drawbacks:

• It cannot always distinguish between past and present infection.
• False positives may occur in other infections.
• Accuracy improves when two tests are done 7–10 days apart to check rising antibody levels.

When Should You Get a Widal Test?

• Persistent fever lasting more than 5–7 days.
• Abdominal discomfort and diarrhoea or constipation.
• Recent exposure to contaminated food or water.
• When a doctor suspects typhoid based on clinical symptoms.

Why Reading It Correctly Matters

Understanding your Widal test report is not about self-diagnosis but about being informed. Knowing what the titles mean helps you:

• Communicate better with your doctor.
• Avoid unnecessary panic over low titres.
• Understand why repeat testing or other investigations may be needed.

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Final Word

The Widal test remains a valuable tool in diagnosing typhoid fever, especially in regions where the disease is common. The key is to read the report step by step, focusing on O and H antigen titres, and always considering symptoms alongside the results.

If your report suggests a possible infection, follow up with your doctor immediately. Early diagnosis and treatment are crucial in typhoid, and proper testing ensures faster recovery.