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

The Widal test is one of the most commonly prescribed blood tests in India to diagnose typhoid fever. Despite its widespread use, many patients struggle to interpret its results. Confusing terminologies like 'O titre', 'H antigen', and dilution ratios like 1:80 or 1:160 often lead to panic or self-misdiagnosis. This blog simplifies each component of a Widal test report so you can understand what it really means and how to act on it—with the right clinical support.

What Is a Widal Test?

The Widal test is a serological test used to detect the presence of antibodies (agglutinins) in the blood against Salmonella typhi, the bacteria responsible for typhoid fever. The test measures the immune response to two types of antigens:

• O (somatic) antigen
• H (flagellar) antigen

In addition to Salmonella typhi, the test may also check for antibodies against paratyphoid strains (AH and BH). The results are expressed in titration format (like 1:80, 1:160) based on the dilution level at which agglutination (clumping) occurs.

Also Read: What Tests are Done for Typhoid

When Is Widal Test Recommended?

• Typically prescribed after 5–7 days of continuous fever
• Useful in resource-limited areas where blood cultures aren’t easily available
• Always considered alongside clinical signs and other tests like CBC or CRP

Key Terms in Widal Report

• O Antigen: Indicates current or recent infection
• H Antigen: Indicates past infection or exposure (including vaccination)
• AH/BH Antigen: For Salmonella paratyphi A and B
• Titre: Level of antibody in blood, represented as a dilution ratio (e.g., 1:80, 1:160)

Step-by-Step Reading of Widal Report

1. Locate O Antigen Titre: Values greater than 1:80 are often considered significant
2. Check H Antigen Titre: A result of more than 1:160 suggests past or ongoing exposure
3. Check AH and BH Titres: Useful if paratyphoid is suspected
4. Interpret Together: Positive O + H titres may suggest active infection
5. Consider Local Context: Endemic areas may have higher baseline titres; clinical correlation is key

What Do Positive Results Mean?

• O >1:80 and H >1:160: Suggests possible typhoid infection
• Only H positive: Could indicate previous infection or vaccination
• AH/BH positive: May indicate paratyphoid fever

Always consider test timing (after 5–7 days of fever) and symptoms for accurate interpretation.

Common Pitfalls in Interpretation

• False positives due to previous typhoid or vaccination
• False negatives if done too early in the infection
• Misinterpretation of low titres as active disease
• Lack of clinical correlation with other diagnostics like CBC or CRP

Should You Self-Diagnose Using Widal Alone?

No. The Widal test is only a supportive tool. A definitive diagnosis should be based on blood culture or comprehensive clinical evaluation. Misinterpreting a Widal test can lead to unnecessary antibiotic use or missed diagnoses.

How Orange Health Labs Supports Diagnosis

• At-home Widal test with 60-minute sample collection
• Bundled testing options with CBC, CRP, and fever panels

The Widal test remains a relevant and widely used diagnostic tool in India, but interpreting it requires more than just reading numbers. Understanding the difference between O and H titres, the importance of testing timing, and pairing it with symptoms and other diagnostics can lead to smarter, faster treatment decisions. For safe, accurate at-home testing, Orange Health Labs provides end-to-end diagnostic support with certified accuracy.

Book your Widal test online today and get fast, doctor-reviewed results from home.