Widal (Slide Agglutination) Test
Widal (Slide Agglutination) Test
The Widal Test (Slide Agglutination Method) is a serological test used for the diagnosis of typhoid fever, which is caused by Salmonella typhi and Salmonella paratyphi. The test detects agglutinating antibodies (O and H antigens) in a patient's blood sample, which develop in response to infection.
Typhoid fever is a serious bacterial infection transmitted through contaminated food and water, leading to high fever, abdominal pain, and systemic complications. The Widal test remains widely used in resource-limited settings due to its cost-effectiveness, although newer diagnostic methods like blood culture and PCR provide greater accuracy.
What is the Widal Test Used For?
- Diagnosing typhoid and paratyphoid fever in symptomatic individuals.
- Screening for past exposure to Salmonella infections.
- Assessing antibody response in suspected cases of enteric fever.
Symptoms Indicating the Need for the Test
Fever
Fatigue
Stomach pain
Headache
Diarrhoea
Cough
Loss of appetite
Spots all over the body (rose-shaped)
Preparation for the Test
No fasting is required before the test. A blood sample is drawn from a vein in the arm. Patients should inform their doctor about recent vaccinations or infections, as these may affect results.
Interpretation of Test Results
A rising antibody titer in samples taken 7-10 days apart is more reliable than a single test result.
|
Antibody Titer |
Interpretation |
|
Less than 1:80 |
No significant antibody levels; typhoid unlikely. |
|
1:80 to 1:160 |
Possible typhoid infection; clinical correlation needed. |
|
Greater than 1:160 |
Suggestive of active typhoid fever; further confirmation required. |
FAQs
How does the Widal Slide Agglutination test work?
The test mixes patient serum with Salmonella antigens on a slide. If agglutination (clumping) occurs, antibodies are present.
Is the Widal test always accurate?
No, it has limitations due to cross-reactivity with other infections and past vaccinations. Blood culture and PCR tests are more reliable.
What does a positive Widal test mean?
A positive test suggests typhoid fever, but clinical symptoms and repeat testing are needed for confirmation.
What other tests help diagnose typhoid fever?
Blood culture, stool culture, and rapid PCR tests are more accurate alternatives.
Can Widal test detect typhoid early?
No, antibodies take 7–10 days to develop, making early diagnosis unreliable. Blood culture is preferred in the first week of illness.
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